Do plastic vessels require Tevila?
Some Poskim rule plastic vessels require immersion without a blessing. Other Poskim however rule that it does not require immersion. Practically, many are accustomed to not immerse plastic vessels. Others however are accustomed to immerse them without a blessing.
 See Hakashrus 4/25; Ohel Yaakov p. 259; Vedarashta Vechakarta 1/12
 Minchas Yitzchak 3/76-77; Kinyan Torah 2/84 that so is custom; Sheraim Hametzuyanim Behalacha 37/4 says to immerse with a blessing
 The reason: As perhaps any material that can be melted in fire has the same status as glass which requires Rabbinical immersion. [See Darkei Teshuvah 120/14] Nevertheless, a blessing is not to be recited as possibly only those materials explicitly decreed upon by the Sages require immersion. [Minchas Yitzchak ibid, based on Melameid Lehoil 2/49] Furthermore, since there exist forms of plastic that cannot be melted down and reformed, therefore every plastic vessel is a doubt. [See Minchas Yitzchak ibid in asker]
 Melamed Lehoil 2/49; Chelkas Yaakov 2/163; Chayeh Halevi 4/56-3; Tzitz Eliezer 7/37; Beir Moshe 2/53 that one should not be stringent to immerse it; Vayeishev Moshe 2/86-6; Mishneh Halachos 7/110; Divrei Chachamim p. 189 in name of Rav Elyashiv; Yabia Omer 4/8; Yechaveh Daas 3/60; Ohel Yaakov ibid in name of Rav Moshe Feinstein and Rav Henkin
 The reason: As we cannot make new decrees, and since this material was not around in the times of Chazal, therefore, it is not included in the original decree against plastic. [ibid]
 Koveitz Beis Levi Nissan 5756 and Hakashrus 4/25 that so is custom and so was custom of Chazon Ish; However see Ohel Yaakov ibid that Rav Wozer said that initially it should be immersed if possible.
 Yechaveh Daas 3/60 “One who does so is blessed”; Chelkas Yaakov ibid that one who does so is blessed; Kinyan Torah ibid that so is custom