Chapter 4: Insulation-Hatmana on Shabbos

Insulating foods on Shabbos

1. The prohibition against insulating food on Shabbos:[1]

It is forbidden to insulate hot foods on Shabbos. This applies even if the insulation material does not add heat.[2] This applies even if the food is fully cooked and even if further cooking will cause it damage.[3] This applies even if the food was left on the fire from before Shabbos in a permitted way.[4] [Thus, it is forbidden to insulate a hot pot of food on Shabbos even if the pot is on one’s counter and not on a heat source.]

Materials that add heat: It is forbidden to insulate using material which adds heat, even completely cold food, and even before Shabbos, as explained in the previous chapter.

2. The criteria of forbidden insulation-The definition of insulation: 

A. The law if the insulation does not touch the walls of the pot:

If the insulating material does not directly touch the walls of the pot, then it is not considered insulated. See Chapter 3 Halacha 3B for the full details of this matter.

B. How much of the pot must be insulated for it to be considered a prohibited insulation?[5]

If the top of the pot is covered with insulation material [whether the material adds heat or does not add heat] then it is defined as “insulation that does not add heat,” and may thus not be done on Shabbos even if the sides of the pot are not covered with the material. Accordingly, it is forbidden to place a towel or the like on top of a hot pot on Shabbos, whether it is on or off the fire, as doing so is defined as insulation. However, if the pot is off the fire, then it is permitted to surround completely its walls with a towel, leaving its top [meaning its cover] uncovered by the insulation material.[6] However, if the pot is sitting on top of a source of heat [such as a blech, or on top of a pot that is on the blech] then in addition to it being prohibited to place a towel over its top, as well one may not wrap a towel around majority of the pots walls, as this is considered insulation which adds heat which is forbidden to be done even before Shabbos! As well if the food is not fully cooked one may not place insulation even on minority of its walls.

3. The law by Bein Hashmashos of Erev Shabbos?[7] 

It is permitted to insulate food in material that does not add heat by Bein Hashmashos, prior to Tzeis Hakoachavim.[8] [However, if the material adds heat, then it is forbidden to insulate with it in all cases even prior to the start of Shabbos, as explained in the previous chapter.]

If one accepted Shabbos early:[9] One who fully accepted Shabbos prior to [nightfall, or even] sunset, is forbidden to do any Shabbos forbidden activity, even Rabbinical in nature, from that time and on. Hence all the permitted activities that may be done during Bein Hashmashos, are forbidden for him to do from the time he fully accepted Shabbos, even if it is before sunset. Hence, he may not insulate hot foods for Shabbos even in material that does not add heat, even if he does not have any other food to eat for Shabbos.

Q&A What is the meaning of fully accepting Shabbos?[10] In this respect, Shabbos is only considered accepted if one has lit candles and thus accepted Shabbos, or if one has already Davened Maariv, or has answered Barchu, or the majority of one’s Shul has accepted Shabbos[11]. However, if none of the above have been fulfilled, and one simply decided on his own to accept Shabbos early [as is done for Tosefes Shabbos], then he may insulate until the end of Bein Hashmashos.[12]   May one who lit candles do Hatmanah until night?[13] No, as he or she has already accepted all the laws Shabbos, as explained in the previous question.

4. Scenarios in which insulating on Shabbos is permitted:

A. Covering the food/pot in order to conserve its heat:[14]

It is permitted to place a vessel as a covering over a hot pot for the purpose of retaining its heat, if the vessel does not touch the walls [or even the top[15]] of the hot pot.[16]

 

B. Covering the pot in order to guard it:[17]

It is permitted to place a vessel on top of hot food in order to guard it from mice, or so that it not get dirty from the ash.[18]

May one cover the pot even with materials that add heat when his intent is to guard it? Yes.[19] However, some Poskim[20] are stringent in this matter. May one cover the pots in order to prevent his children from touching it and receiving a burn?[21] Yes.

C. Re-insulating on Shabbos a pot that had been insulated before Shabbos?[22]

It is permitted to reinsulate on Shabbos a pot that was insulated[23] from before Shabbos with a material that does not add heat. This applies whether the insulation unraveled on its own or if one actively undid the insulation, such as to take out food. This allowance applies even if at the time that one unraveled the insulation, he did not have in mind to reinsulate it.[24] Furthermore, even initially one may unravel it and then return and insulate it.

Adding more insulation material:[25] One may add more insulation material to the current insulation.

Switching the insulation material:[26] One may remove all of the insulating material placed before Shabbos and place other material there in its place. This applies whether the original insulation was warmer than the new insulation, or if the second insulation is warmer than the first. Even if the pot was only insulated with a sheet, one can remove the sheet and insulate it with a thick blanket.

If the food is not fully cooked:[27] If the pot is standing over a source of heat, then one may only add insulation material if the food is fully cooked. If the food is not fully cooked, then it is forbidden to add any material even to the insulated cover of the pot. [However, if the pot is not on any source of heat, then one may reinsulate it, or add more insulation to it on Shabbos, even if the food is not fully cooked. [28]]

Q&A If the insulation was removed, or unraveled, by Bein Hashmashos, may it be reinsulated after dark?[29] No.[30] The insulation must be intact when the night of Shabbos enters. This applies even if the congregation already accepted Shabbos, and afterwards the insulation unraveled before night, that it may not be reinsulated.[31]   If one insulated the food for purposes of protection, may he then remove the insulation on Shabbos and replace it for purposes of insulation? This matter requires further clarification.[32]   If only part of the pot was insulated before Shabbos, may one add insulation to it on Shabbos? No. One may not add insulation to make it fully insulated.[33]   May one return the insulating material even if he removed it with intent to not return it on Shabbos?[34] Yes.   Must one fulfill the Chazarah conditions in order to be allowed to return the insulation to the pot? No. One is not required to fulfill the Chazara conditions when returning the insulation to the pot.[35] However some Poskim are stringent regarding the opposite case, that one removed the pot from the insulation and now desires to return the pot to the insulation, as will be explained in the next Q&A!   May one reinsulate a pot that was insulated before Shabbos even if he removed the pot from the insulation, or only if he removed the insulation from the pot, leaving the pot in its original area?[36] There are Poskim[37] which say that when the pot was removed from the insulation one must fulfill all the conditions of Chazara to be allowed to return it to the insulation. However, this does not seem to be the opinion of the Alter Rebbe or the Mishneh Berurah. May one re-insulate a pot or add insulation to a pot that was insulated before Shabbos even if the food is not fully cooked?[38] If the pot is standing over a source of heat, then it may only be reinsulated if the food is fully cooked, as by returning the insulation one speeds up the cooking. However, if the pot is not on any source of heat, then it is always allowed to re-insulate or add more insulation on Shabbos, even if the food is not fully cooked, as this does not make it cook any further.[39] May one add other pots that were not insulated before Shabbos into the insulation of an insulated pot? No.[40] May one add food to an insulated pot and then return the insulation?[41] If the insulated pot is a Keli Rishon, based on the previous Q&A, it is forbidden to do so.

D. Keli Sheiyni-Insulating on Shabbos a hot food which has been transferred to a second pot:[42]

If one removed the food from its original pot and placed it into a second pot, then it is permitted to insulate the second pot.[43]

If one poured the food back into its original pot:[44] Furthermore even if one goes back and returns the food into the original pot, it is permitted  to insulate it.

Materials that add heat: The above allowance only applies to using insulation material that does not add heat, however material which adds heat, is forbidden to insulate with, even completely cold food, and even before Shabbos.

Q&A Does this permission of a Keli Sheiyni apply even if the food is a solid substance [“Davar Gush”]?[45] Yes. This applies even according to those Poskim that are normally stringent regarding a Davar Gush in other Shabbos laws.[46] May one place hot water on Shabbos into an insulation thermos?[47] Yes, as the insulation is not being done to the original pot.[48] May one place hot water in a stomach pad? Yes. May one insulate a food that was placed from one Keli Rishon to another empty Keli Rishon?[49] No.[50] However, there are Poskim[51] that are lenient in this matter. Likewise, there are Poskim[52] that are lenient to allow pouring water into a thermos that was on a Keli Rishon.[53]  May one insulate a bottle of food that was entered into a Keli Rishon and became hot?[54] No.

E. May one use a thermos on Shabbos?

Using a thermos on Shabbos involves pouring hot water into the thermos for the purpose of insulating its heat for an extended period of time, and hence touches upon the question of insulation. The following is the ruling:

It is Rabbinically forbidden to insulate hot foods or liquids on Shabbos even if the insulation does not add heat to the food, but simply conserves it.[55] This however only applies so long as the hot food or liquid remains in the original vessel that it was cooked in [i.e. Keli Rishon]. If, however, the food or liquid is poured into a second vessel, then there is no prohibition against insulating the second vessel on Shabbos.[56] Accordingly, there is no prohibition against using a thermos on Shabbos, and pouring boiling water into it for the sake of conserving the heat of the liquid.[57] For the same reason, it is likewise permitted to enter hot water into a stomach pad on Shabbos.[58]

F. Insulating cold food on Shabbos:[59]

It is permitted to insulate completely cold foods on Shabbos with materials that do not add heat, in order so it not become too cold, or in order to remove its coldness. ([Furthermore] if the food cooled off to the point that it is not Yad Soledes, it is permitted to insulate it even while it is still in the original pot.[60]) Materials that add heat:[61] It is forbidden to insulate even completely cold foods using material that add heat to the food. [This applies even if the material is not defined as Hatmana Shemosif Hevel, nonetheless, so long as it adds heat to the food, it is forbidden.[62]]

May one on Shabbos place a cold bottle into a hot pot of water that is off the fire?[63] If the food will not be able to get heated to the point of Yad Soledes[64], or will but does not contain a cooking prohibition [such as the food is fully cooked and does not contain liquid, or the water is a Keli Sheiyni and the bottle contains only liquid], then if it is not completely submerged within the water, such as if the bottle is floating and the upper part of the bottle is revealed, then it is allowed.[65] However if it is completely submerged within the water, then it is only allowed if heat will not be added to the food, and rather is being placed there only to retain its current heat.[66] This applies even by a Keli Sheyni.[67]

5. Sealing the cover of a pot of food on Shabbos:[68]

It is permitted to seal the lid of a pot in order to retain its heat. This applies even if the food is not fully cooked, so long as it is off the fire.

6. What is the law if one insulated food on Shabbos?[69]

If the food became hotter due to the insulation it is forbidden.[70] If the food remained the same temperature, then if the material used is defined as “does not add heat,” it is permitted.[71] If the material is defined as material that adds heat then even if it did not add heat to the food, there are Poskim[72] which side that it is nevertheless prohibited [even if the food was fully cooked and Mitztamek Vera Lo]. Others[73] argue on this ruling and permit the food [if it was fully cooked, and further cooking was detrimental towards the food] and heat was not added towards it.

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[1] Admur 257:2; Michaber 257:1

[2] The reason: [Now,] even though [insulating with material that does not increase heat] is not similar to [insulating with] ember at all, and thus why then is it forbidden? [Nevertheless, it is forbidden] due to a decree that perhaps when one comes to remove the pot from the stove in order to insulate it with material that does not increase heat, he will find that the pot is cold, and will forget that it is Shabbos and reheat it on the fire, hence being liable for [the prohibition of] cooking. [Now this suspicion only applies according to those which hold that reheating a cooked food constitutes cooking, however] according to those which say that there is no cooking [prohibition involved] with [reheating] something that was already cooked even if it became cold afterwards, as will be explained in chapter 318, [nevertheless even according to them insulating on Shabbos is forbidden due to a different worry as] we are worried that one may stoke the coals in order reheat it and will thus be liable for [the prohibition] of making a fire. [Admur ibid; Shabbos 51a; Beis Yosef in name of Rashi; M”A 257:1 in name of Rosh; M”B 257:1] Thus, it is forbidden to insulate even foods that are dry and do not have a cooking prohibition, due to the above worry of stoking the coals. [Shaar Hatziyon 257:3]

Other opinions: Some Poskim rule that the reason for why insulating on Shabbos is forbidden is because one may come to insulate in ember. [Rambam Hilchos Shabbos 4:3] See Lechem Mishneh ibid that explains the source of the Rambam from the above Gemara and how he interprets it differently.

[3] Admur 257:3; “Even food which is completely cooked, and further cooking will condense it in a way that is damaging to it, is forbidden to be insulated from when it becomes dark [after Bein Hashmashos, by the definitive beginning of Shabbos], even with a material that does not add heat”; Michaber 257:2

[4] Admur 253:14 “If the pot was in the Kirah and on Shabbos one comes to take it out from the Kirah and insulate it, even if he wants to use a [form of insulation, such as] pillows or blankets or other clothing, which does not add heat but just retains the heat, it is [nevertheless] forbidden, as it is considered like one is insulating the pot now on Shabbos for its first time, which is forbidden [to be done] even if the insulation does not add heat.”

[5] Admur in Mahadurah Basra 259; Ketzos Hashulchan 71 footnote 34; Shabbos Kehalacha Vol. 2 page 56-58; Chazon Ish 37:19 forbids any form of insulation, even minute, on Shabbos; See Piskeiy Teshuvos 257:12

Background: This ruling is based on the explanation of the Alter Rebbe in the Mahadurah Basra that there is a difference between insulation that adds heat and insulation that does not add heat, that by the latter, the main aspect is the top of the pot, as that is how the heat is mainly guarded. This ruling in the Mahadurah Basra thus seems to be a retraction of his ruling in 257:4, and in the summary brought in chapter 259. This ruling is brought as well by the Ketzos Hashulchan chapter 71 note 34. Other Poskim however rule that by this form of insulation it is only problematic if the entire pot has been covered. So rules also the Shemiras Shabbos Kihilchasa, following the Alter Rebbes ruling in his Shulchan Aruch.

Ruling of Admur in Shulchan Aruch: It is only forbidden to completely insulate the pot within the insulation material on Shabbos. [Admur 257:4] Even according to the Michaber we do not rule Hatmana Bemiktzas regarding insulating on Shabbos. [Kuntrus Achron 257:2]

Other opinions: Some Poskim rule that this follows the same law as Hatamana on Erev Shabbos and hence according to the Michaber it is forbidden even to partially insulate the pot while according to the Rama it is only forbidden if completeluy insulated. [Beir Heiytiv 253:17; M”B 253:69] Others rule that according to all it is only considered insulation if it is completely insulated. [Kuntrus Achron 257:2; SSH”K 1:66; Or Letziyon 17:12] Practically the custom of the world is to be lenient like the Rama. [Piskeiy Teshuvos ibid]

[6] This latter ruling holds true even according to the Alter Rebbes SH”A as stated in 253:14: “However if [on Shabbos one wants to insulate the pot by having] the pillows and blankets wrapped [only] around the walls of the pot, but leaving its top revealed, then it is permitted to be done as this is not considered [the prohibited form of] insulation.”

[7] Admur 257:2 “By Bein Hashmashos, even though it is questionable if it is considered nighttime [and thus perhaps Shabbos has already begun, nevertheless], one is permitted to insulate [food] in something that does not add heat.”; 261:2; Michaber 257:1

[8] The reason: The reason for why this is permitted is because pots are usually still hot by Bein Hashmashos, as close to Bein Hashmashos the pots are removed from the fire and thus [at Bein Hashmashos] there is no need to worry that perhaps the food has cooled off and one will come to reheat it. [Admur ibid]

^[9] Admur 261:3; Shabbos Kehalacha Vol. 2 page 2-4

^[10] Admur 261:2; Kuntrus Achron 261:3; Ketzos Hashulchan 77 footnote 11; Shabbos Kehalacha Vol. 2 page 2-4; See Piskeiy Teshuvos 261:8

^[11] Admur 261:4

^[12] Other opinions: The Igros Moshe [4:74-1] rules stringently that today it is never practical to insulate by Bein Hashmashos as certainly most of the community has accepted Tosefes Shabbos before Shekiah. However Rav Farkash in the supplements [pages 69-72] argues and disproves this with very strong supports, and so seems to be the ruling as written above, that there is a difference between Tosefes Shabbos and Maariv and the like.

[13] Igros Moshe 4:74-1; Ketzos Hashulchan 77 footnote 11; M”B 263:43; Shabbos Kehalacha Vol. 2 page 2-4; Piskeiy Teshuvos 261:8

Other opinions: Some opinions rule one may do all Melacha’s permitted by Bein Hashmashos even after lighting andles. [Chasam Sofer 65; Shoel Umeishiv Telisa 2:23; Erech Shay 263:17; Meishiv Davar 1:22; Tehila Ledavid 261:10 leaves this matter in question]

[14] Admur 257:4“It is forbidden to place a vessel as a covering over a hot pot for the purpose of retaining its heat (if the pot is entirely insulated underneath the vessel), unless the vessel is wide enough to the point that its walls do not touch the sides of the pot, in which case there is no [prohibition of] insulation being done at all.”

[15] Based on the ruling of the Mahadura Basra 259 it is also necessary that the top of the pot does not touch the top of the lower pot. [Ketzos Hashulchan 71 footnote 38]

[16] Meaning there is space between the walls of the smaller pot and the walls of the large pot which is sitting over it.

[17] Admur 257:4; Michaber 257:2; See Piskeiy Teshuvos 257:3 and 6

[18] The reason: As this is not considered insulating for retaining of heat, but is rather is a measure of guarding and [is like] placing a cover on top of a pot. [Admur ibid]

[19] Az Nidbaru 5:15; Rav SZ”A in Maor Hashabbos 1:11; Piskeiy Teshuvos 257:7; However see Minchas Shlomo 2:34-20

[20] Toras Shabbos 257:9

[21] Piskeiy Teshuvos 257 footnote 45

[22] Admur 257:8 “If one insulated [a pot] from before Shabbos with a material that does not add heat, and it unraveled before Shabbos, whether it unraveled on its own, or if one unraveled it with his hands and one had in mind to go back and re-insulate it before Shabbos or after Shabbos has begun, then it is forbidden to re-insulate it once Shabbos has begun [past Bein Hashmashos], as this is considered like one is initially insulating [the pot] on Shabbos [which is forbidden to do], since when Shabbos came in it was not insulated. However, if it was insulated in the beginning of the entrance of (Shabbos) the night, and then afterwards it unraveled, it is permitted to re-insulate it. This applies whether it unraveled on its own or if one did so with his hands, even if [at the time that he unraveled it] he did not have in mind to go back and insulate it. [Furthermore] even initially one may unravel it and then return and insulate it.”; Michaber 257:4; See Piskeiy Teshuvos 257:7-8; 259:1

^[23] Based on the definition of insulation for material that does not add heat. A pot is only considered to have been insulated from before Shabbos if its cover was insulated, whether or not its sides were insulated.

[24] Seemingly this includes even if one specifically had in mind to not reinsulate it, and then changed his mind, that he is allowed to do it. So rules the Aruch Hashulchan 257:20; and is implied from the Tehila Lidavid. [Shabbos Kehalacha vol. 2 page 63-64]

[25] Admur ibid “If one wants to add [to the insulating material] on Shabbos other materials which do not add heat, he may do so.”

[26] Admur ibid “As well if one wants to remove all of the insulating material [placed before Shabbos] and place other material there in its place, whether the original insulation is hotter than the second one, or if the second insulation is hotter than the first. Even if the pot was only insulated with a sheet, one can remove the sheet and insulate it with a thick blanket.”

[27] Admur ibid “This only applies if the food was fully cooked, however if it is not fully cooked and is insulated on top of a Kirah (that has had its coals swept), then it is forbidden to even add on to the cover, as this addition causes to speed up the cooking due to the coals.” See M”A 257

[28] Based on Admur 257:8; 318:14; M”A 257; Peri Megadim; However see 254:4 which rules it is forbidden to place uncooked foods on top of an insulated pot; Tehila Ledavid 254:4 establishes the case there to be referring to a pot that is on the fire and is insulated in a permitted way, such as with a board over the top of the pot, and the insulation is thus not touching the walls of the pot.

Other opinions: Some Poskim rule it is forbidden to add or reinsulate whenever the food is not fully cooked even if it is not on a source of heat. The reason for this is because the insulation delays the cooling down of the food and during this time the food is able to cook more. [M”B in Biur Halacha 257:4 “Gorem Lah”; Beis Meir; Nehar Shalom; Mor Uketzia]

[29] See Piskeiy Teshuvos 257:7; Shabbos Kehalacha 11 footnote 83 [p. 62]

[30] Shaar Hatziyon 257:25 in name of Gr”a; wording of Michaber is “at dark”; Damesek Eliezer on Gr”a; Shabbos Kehalacha ibid; Piskeiy Teshuvos ibid

Ruling of Admur: Admur ibid writes “However if it was insulated in the beginning of the entrance of (Shabbos) the night”. Seemingly the novelty in the additional words “Shabbos” is that the Alter Rebbe is saying that once Shabbos has begun, which is after sunset, if it was insulated and unraveled, one may reinsulate it on Shabbos. However, since these words were placed in parentheses, Tzaruch Iyun as to how we should rule. Practically in Shabbos Kehalacha ibid, after bringing the sides for the issue, concludes that one should be stringent. The Piskeiy Teshuvos 257 footnote 51 interprets the added word Shabbos in parentheses to include if the congregation accepted Shabbos upon themselves and does not include Bein Hashmashos. The reason for this is because it is permitted toi insulate during Bein Hashmashos, and this it is not yet considered as if it was insulated into Shabbos. However, it is forbidden to insulate once Maariv was prayed and hence it is considered the pot was insulated into Shabbos.

[31] See Piskeiy Teshuvos ibid that writes “it’s possible in such a case that it is permitted to do so”; However, Shabbos Kehalacha ibid concludes not to do so.

[32] Piskeiy Tehsuvos 257 footnote 52 writes it is forbidden. However, Tzaruch Iyun as perhaps the reason for allowing the reinsulation is because the pot will certainly still be warm if it contained Hatmana material before Shabbos, and hence it would make no difference as to why he insulated it.

[33] Seemingly this applies even according to Admur as perhaps we follow his ruling in the Mahadurah Basra only to be stringent not to cover the pot on Shabbos and not to be lenient to allow covering the rest of the pot on Shabbos if the top was covered before Shabbos. Vetzrauch Iyun!

[34] Aruch Hashulchan 257:20; Shabbos Kehalacha; Piskeiy Teshuvos 259 footnote 1

[35] Admur ibid; Tehila Ledavid 257:4

^[36] Shabbos Kehalacha Vol. 2 page 64; Piskeiy Tehsuvos 259:1

^[37] Tehila Lidavid 257:4; 259:2; Elya Rabah 259:9 in the name of the Lechem Mishneh [not on the Rambam]

^[38] Shabbos Kehalacha Vol. 2 page 60; See Piskeiy Teshuvos 257:7 footnote 53 that discusses the dispute on this matter

[39] Based on Admur 257:8; 318:14; M”A 257; Peri Megadim; However see 254:4 which rules it is forbidden to place uncooked foods on top of an insulated pot; Tehila Ledavid 254:4 establishes the case there to be referring to a pot that is on the fire and is insulated in a permitted way, such as with a board over the top of the pot, and the insulation is thus not touching the walls of the pot.

Other opinions: Some Poskim rule it is forbidden to add or reinsulate whenever the food is not fully cooked even if it is not on a source of heat. The reason for this is because the insulation delays the cooling down of the food and during this time the food is able to cook more. [M”B in Biur Halacha 257:4 “Gorem Lah”; Beis Meir; Nehar Shalom; Mor Uketzia]

[40] Admur 318:14; Shevisas Shabbos Mevashel 105; Chazon Ish 37:17

Other opinions: Some Poskim rule it is permitted to do so. [M”B 318:51; See Minchas Shlomo 2:34-18; Piskeiy Teshuvos 257:8]

[41] See Piskeiy Teshuvos 257 footnote 54

[42] Admur 257:9“It was only made forbidden to insulate on Shabbos with material that does not add heat, when one is insulating the actual pot in which the food was cooked in, as then the decree that one may come to heat it up is applicable. However, if one removed the food into another pot, it is permitted to insulate it.”; Michaber 257:5; See Piskeiy Teshuvos 257:9

[43] The reason: As the food has already cooled off a little in the walls of the second pot, and the Sages only forbade insulating if the food is [still] hot in the original pot that it was cooked in. [Admur ibid]

[44] Admur ibid “even if one goes back and returns the food into the original pot, it is permitted to insulate it (being that the food has already cooled off a little in the walls of the second pot, and the Sages only forbade insulating if the food is [still] hot in the original pot that it was cooked in.)”; M”A 257; M”B 257:28

^[45] Shabbos Kehalacha Vol. 2 page 52; Piskeiy Teshuvos 257:9; Migdanos Eliyahu 1:83; Chut Hashani 257:6

[46] The reason: As even according to those Poskim that are stringent by a Davra Gush, nevertheless he has performed which cools off the food and hence there is no longer a worry that he may forget that it is Shabbos due to his desire to heat up the food.

^[47] Kuntrus Achron 257:1 “Even if it does not cool it off”; Peri Megadim 257 M”Z 5 in opinion of Rambam; Givas Levona 25; Keren Ledavid 1:77; Zekan Ahron 2:14; Darkei Chaim Veshalom 421; Ketzos Hashulchan 71 footnote 36; Chelkas Yaakov 84; Or Letziyon 2:17-11; Igros Moshe 1:95; Betzeil Hachochmah 2:74; Beir Moshe 1:12; Minchas Shlomo 2:8; Tzitz Eliezer 11:29; Chazon Ish 37:32; Even Yisrael 9:8; Shabbos Kehalacha Vol. 2 page 66; Piskeiy Teshuvos 257:9

Other Poskim: Some Poskim are stringent based on the opinion of Rashi that requires cooling down, to prohibit the use of a thermos being that one does not intend to cool off the water. [Levushei Mordechai 2:55; Tzafnas Paneiach 2:27; Melamed Lehoil 1:45; Shevet Halevi 1:93] Even one who desires to be stringent can simply avoid filling the water until the top [Pnei Shabbos in name of Divrei Yatziv] or through pouring the water into a Keli Sheiyni and then into the thermos. [Levushei Mordechai ibid].

[48] The reason: A the thermos is considered a Keli Sheiyni, and the Sages did not decree against it even if it does not cool off the food. [Igros Moshe ibid based on Rambam] Furthermore, doing so is permitted even according to Rashi that requires cooling down, as the entire prohibition is in covering the thermos, and it is permitted to cover it just like it is permitted to cover any vessel. [See Igros Moshe ibid; Chazon Ish ibid that there is never a prohibition in pouring from one vessel to another even if it insulates]

[49] Piskeiy Teshuvos 257:9

[50] Piskeiy Teshuvos 257:9; Shabbos Kehalacha 11 footnote 68

[51] P”M 257 M”Z 5; Implication of Admur 257:9 “And the Sages only prohibited in the Keli Rishon that it was cooked in”. See Shabbos Kehalacha 11 footnote 68

[52] Chazon Ish 37:32; Piskeiy Teshuvos 257:6

[53] The reason: As there is no prohibition of Hatmana in pouring from one vessel to another even if it insulates, and the entire prohibition of Hatmana is to take insulating material and wrap it around the vessel.

[54] Piskeiy Teshuvos 257:9

[55] Admur 257:2; Michaber 257:1; Shabbos 51a

The reason: This is due to a decree that perhaps when one comes to remove the pot from the stove in order to insulate it with material that does not increase heat, he will find that the pot is cold, and will forget that it is Shabbos and reheat it on the fire, hence being liable for [the prohibition of] cooking.

Other opinions: Some Poskim rule that the reason insulating on Shabbos is forbidden is because one may come to insulate in ember. [Rambam Hilchos Shabbos 4:3; See Lechem Mishneh ibid]

[56] Admur 257:9; Michaber 257:5

^[57] Kuntrus Achron 257:1 “Even if it does not cool it off”; Peri Megadim 257 M”Z 5 in opinion of Rambam; Givas Levona 25; Keren Ledavid 1:77; Zekan Ahron 2:14; Darkei Chaim Veshalom 421; Ketzos Hashulchan 71 footnote 36; Chelkas Yaakov 84; Or Letziyon 2:17-11; Igros Moshe 1:95; Betzeil Hachochmah 2:74; Beir Moshe 1:12; Minchas Shlomo 2:8; Tzitz Eliezer 11:29; Chazon Ish 37:32; Even Yisrael 9:8; Shabbos Kehalacha Vol. 2 page 66; Piskeiy Teshuvos 257:9

The reason: As the thermos is considered a Keli Sheiyni, and the Sages did not decree against it even if it does not cool off the food. [Igros Moshe ibid based on Rambam] Furthermore, doing so is permitted even according to Rashi who requires cooling down, as the entire prohibition is in covering the thermos, and it is permitted to cover it just like it is permitted to cover any vessel. [See Igros Moshe ibid; Chazon Ish ibid that there is never a prohibition in pouring from one vessel to another even if it insulates]

Other Poskim: Some Poskim are stringent based on the opinion of Rashi that requires cooling down, to prohibit the use of a thermos being that one does not intend to cool off the water. [Levushei Mordechai 2:55; Tzafnas Paneiach 2:27; Melamed Lehoil 1:45; Shevet Halevi 1:93] Even one who desires to be stringent can simply avoid filling the water until the top [Pnei Shabbos in name of Divrei Yatziv] or through pouring the water into a Keli Sheiyni and then into the thermos. [Levushei Mordechai ibid].

[58] M”B 326:6 in opinion of Rashi and Admur 326:5 who only records Rashi’s opinion

The reason: As there is now no suspicion that it will spill. As well, there is no medication prohibition involved here as is seen from the fact that Admur ibid makes no mention of it.

Other opinions: According to the reason of Tosafus, even a closed bottle is forbidden to be placed on the body, as it is considered Refua. [M”B 326:19 in name of Karban Nesaanel] Thus, some Poskim rule one may only be lenient on Shabbos in a time of great need or pain. [M”B 326:19; Beir Moshe 1:33-15]

[59] Admur 257:9 “(If the food cooled off to the point that it is not Yad Soledes, it is permitted to insulate it even while it is still in the original pot) and certainly it is permitted to insulate completely cold food in order so it not become too cold, or in order to remove its coldness”; 318:23; Michaber 257:6; See Piskeiy Teshuvos 257:9

^[60] Admur ibid [parentheses in original]; see also Kuntrus Achron 1 that leaves in Tzaruch Iyun; M”A 257:14 “Its possible…”; M”B 257:31 [Allows in case of need];

May one rely on this even initially? Some Poskim rule one should only be lenient to insulate food, which is still hot but not Yad Soledes, within the original pot, if it is a pressing situation. [Mishneh Berurah 257:28; Admur here places in parenthese and in Kuntrus Achron 257:1 he leaves this ruling with a Tzaruch Iyun] Rav Farkash rules likewise being that even the Alter Rebbe placed this ruling of the Magen Avraham in parentheses. [Shabbos Kehalacha Vol. 2 page 53] Other Poskim are lenient even initially. [Chazon Ish 37:31; Shevet Halevi 8:166; see Piskeiy Teshuvos 257:10]

^[61] Admur ibid “However, all the above is only [allowed] when using insulation material that does not add heat, however material which adds heat is forbidden to insulate with. This applies even with completely cold food, and even before Shabbos.”

[62] Mahadura Basra for chapter 259; p. 878 in new Shulchan Aruch; M”B 258:2; Sheivet Halevy 5:31; Shabbos Kehalacha Vol. 2 page 54-55 and 65 concludes as Mahadurah Basra that it is forbidden; Piskeiy Teshuvos 258:2

Ruling of Admur in Shulchan Aruch: In 318:23 Admur rules that one may immerse a bottle of cold water completely in a Keli Sheiyni. Likewise in 254:4 Admur implies that if a food is fully cooked one may return the insulation even if it is on top of a hot pot, hence implying that one may add heat. However, see Tehila Ledavid 254:4 that establishes this case to be referring to a pot that is on the fire and the insulation was done over a wood board and is hence not defined as insulation at all. Based on this one cannot bring a proof from 254:4 regarding how Admur would rule regarding actual insulation. 

^[63] Mahadura Basra for chapter 259; p. 878 in new Shulchan Aruch; M”B 258:2; Sheivet Halevy 5:31; Shabbos Kehalacha Vol. 2 page 54-55 and 65 concludes as Mahadurah Basra that it is forbidden; Piskeiy Teshuvos 258:2

[64] M”B ibid

^[65] M”B ibid “if top is revealed”; Sheivet Halevy 5:31 and other Poskim based on the rules explained in this chapter.

[66] M”B 258:2 regarding if one’s intent is to heat up the food and Shaar Hatziyon 258:7 regarding if one’s intent is simply to remove its coldness; Sheivet Halevi ibid

Other opinions: Some Poskim rule it is forbidden in all cases to submerge the bottle even if one’s intent is simply to thaw it down and not add heat. [Chazon Ish 37:17]

^[67] See Piskeiy Teshuvos ibid

[68] Admur 318:14 “It is allowed to seal the lid [of the upper pot] with dough in order to retain its heat if he has dough that was kneaded yesterday [and was designated for this purpose and is thus not Muktzah].”

^[69] M”B 257:8, 10, 13; Shabbos Kehalacha Vol. 2 page 59-60; Piskeiy Teshuvos 257:4

[70] See M”B 257:8

[71] M”B 257:8 in name of M”A; Shaar Hatziyon 257:6

^[72] Rav Akivah Eiger, brought in Mishneh Berurah Shaar Tziyon 257:6. However he concludes with a Tzaruch Iyun.

^[73] Piskeiy Teshuvos 257 footnote 30; Rav Farkash argues to permit this, although he does practically rule this way in Shabbos Kehalacha.

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