2. The definition of insulation

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2. 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 pot, then it is not consider insulated. See Chapter 1 Halacha 3A.

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

See Q&A below


1. How much of the pot must be insulated for it to be considered a prohibited insulation?

See note[1] for an elaboration on the different opinions on this. The following is the final ruling as ruled by Rav Farkash in Shabbos Kehalacha: On Shabbos itself it is forbidden to insulate with either material that adds heat or material that does not add heat. The following is the definition of these insulations:

· By material that adds heat:[2]

Majority of the walls of the pot: One should Lechatchilah consider it to be prohibited insulation even if only majority of the walls of the pot are covered, even if its top is uncovered by the insulation material[3].

However by a pressing situation, or Bedieved, one may be lenient to cover the walls fully if he leave its top uncovered[4] [by the insulation, however it may have its pot cover on it].[5]

Minority of the pot: If only minority of the walls of the pot is covered, then if the cover of the pot is not covered with insulation, it is allowed even Lechatchilah.

In all the above cases placing insulating material which adds heat is only allowed if the food is fully cooked, even if one wants to place it only on minority of its walls. As well any material placed on a pot which is on a stove or other source of heat becomes defined as material which adds heat.

· By material that does not add heat:[6] 

The covering of the top of the pot with insulation material [whether the material adds heat or does not add heat] is what is defined as “insulation that does not add heat,” irrelevant to whether or not the sides have been covered, and may thus not be done on Shabbos.[7] 

Practical Summary:

According to above it is always 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 which does not add heat. However, if the pot is off the fire then it is allowed to surround completely its walls with a towel [or other non-heat adding material-for the definition See chapter 1 Halacha 4] leaving its top [meaning its cover] uncovered by the insulation material[8].

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.


[1] According to the Shulchan Aruch of Admur the ruling is the following: In 453:10 Admur defines insulation as fully covering the entire pot with insulating material. In His words “Even if burning coals surround and are attached to the walls of the pot, [nevertheless] this is not considered [the prohibition of] insulation being that the pot is open from the top, [meaning it has no coals surrounding its top].”Similarly in the Kuntrus Achron here number 3 the Alter Rebbe reiterates and explained this ruling, that only if both the walls and the top [meaning the pot cover] is insulated with material is it considered insulation. This ruling is also repeated here in Halacha 4 and in the summary of the laws of insulation brought in Chapter 259, at the very end, and is the simple understanding in chapter 253 Halacha 14. The Sheivet Haleivi rules like this opinion, and does not make mention of the Mahadurah Basra.

However, in the Mahadurah Basra for chapter 259 the Alter Rebbe elaborates on the opinions that hold that by insulation which adds heat we do not take the top of the pot into account, and possibly as well this is the way the Rama holds, and thus possibly even if only majority of the walls are covered, it would be considered insulation. Seemingly Rav Shlomo Zalman Aurbach also rules like this opinion.

According to the Michaber the ruling is that by materials that add heat, insulation of any amount is forbidden. According to the Mishneh Berurah it is unclear whether he holds like the ruling of Admur in the Shulchan Aruch, that it must all be covered to be forbidden, or if he rules like the Kuntrus Achron of Admur that even insulating majority of the walls is not allowed.

[2] Shabbos Kehalacha Vol. 2 page 14-24

[3] This is based on the Mahadurah Basra where the Alter Rebbe brings up the possibility that this is the definition of insulation, and thus we rule Lechatchilah to be stringent like this opinion.

[4] As if one covers the top this is considered insulation which does not add heat, which is forbidden to initially do on Shabbos.

[5] This is based on the ruling in the Shulchan Aruch.

[6] 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

Ruling of Admur in Shulchan Aruch: It is only forbidden to comepletly insulate the pot within the insulation material on Shabbos. [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]

[7] 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.

[8] 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.”

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