Translation:Shulchan Aruch/Orach Chaim/257
1. The Laws of Insulating a Pot of Hot Food, containing 8 Seifim: Hatmana (definition: insulating a pot of hot food) may not be done on Shabbos even with a substance that does not increase heat. However, during the time-frame that is questionable if it’s night (Bein Hashemashos), Hatmana may be done. Hatmana may not be done in a substance that adds heat, even while it is yet day (before Shabbos). If one did Hatmana in a substance that adds heat, the food is forbidden even after the fact. But this specifically refers only to cold food heated (by Hatmana) or (cooked food) improved by further cooking, but if it only retained its original warmth, it is permitted (to eat the food). RAMA: There are those who say that if one forgot and did Hatmana accidentally with a substance that adds heat, it is permissible to eat. [Ha'gahos Mordechai]. And there are those who say, that all this is only forbidden when it is done for the night (meal), but if the Hatmana is done [on Friday] for the following day, while it is still day, it is permissible to do Hatmana in a substance which adds heat. [Mordechai, beginning of the chapter 'Kira'; Beis Yosef, end of Siman 253 in the name of Shbolei Leket]. After the fact one can rely on this opinion provided one does not become accustomed to doing so.
2. One may not do Hatmana on Shabbos even for food that is fully cooked, even with a substance that does not add heat. Nevertheless, one is permitted to place an object over food to protect it from mice and from dust, since this is not Hatmana for retaining heat; rather it is for protective purposes and is like putting a lid on a pot. [See above, Siman 253].
3. The following substances add heat: olive waste or sesame waste, manure, salt, lime and sand, – whether wet or dry. The following three substances add heat when wet: straw, zagin (definition: Grape refuse after pressing), mochin definition: according to the Mishnah Berurah, this is any soft material, such as cotton, soft tufts of wool torn from lambs, or shredding of worn clothing), and grasses. The following substances do not add heat: clothing, fruits, dove downs (or other feathers), worn linen fibers, and carpenter’s shavings (the fine scraps of wood that fall from wood when planed). RAMA: There are those who say that Hatmana is permitted with 11) rocks, even though they add heat, since rabbinical decrees were not enacted in unusual circumstances. [Tosefos; Mordechai beginning of paragraph Lo Yachpor]
4. Even though Hatmana is forbidden on Shabbos even with a substance that does not add heat, if Hatmana was done before Shabbos and (the pot) became uncovered after dark, it is permitted to cover it again. Similarly, one may add to it [more insulation] on Shabbos, if he wishes. Also, one may remove (the coverings) entirely and replace them with others, if he wishes. This holds true whether the first (coverings) retain more heat than the second, or whether the second retain more heat than the first. Even if (the pot) was only covered with a sheet, he may remove and replace it with a thick woolen cloak. All this is on condition that the food is fully cooked, but if it is not fully cooked then even adding to the covering is forbidden, since such an addition causes (additional) cooking.
5. If one transfers food on Shabbos from the pot in which it was cooked to another pot, [then] Hatmana may be done with a substance that does not add heat.
6. One is allowed to store something cold in something that does not add heat so that it doesn’t get even colder or in order to take away its chill. But if it does add heat, even to store something completely cold even prior to Shabbos it is forbidden.
7. Hatmana is forbidden even if the food is fully cooked and Mitztamek ve’ra lo [meaning: Shrinking/drying out through cooking to its detriment]. RAMA: This is the opinion we follow. There are those who are lenient and say that Hatmana is permissible if the food is either completely raw or fully cooked, just as She’hiya (is permissible), as was explained above in Siman 253. In a place where their custom is to be lenient like this opinion, they should not be prevented (from keeping their custom), but other places should not follow this custom.
8. Even though it is permitted to leave a pot standing on a Kirah containing coals according to the conditions explained in Siman 253, however, if the pot is covered with soft materials, even though they do not add heat, they will nevertheless add heat because of the fire underneath [and it is forbidden]. However, in a way that the soft materials do not touch the pot, even though there is fire underneath them, it is permitted since this is not the normal manner for Hatmana. Therefore, where one places a pot on a Kirah or Kupach that contains coals, and the bottom of the pot does not touch the coals, it is called She’hiya and permitted according to the rules laid down in Siman 253. If one places a wide utensil over the pot in such a way that it overlaps the pot and then puts cloths over the wide utensil, this is permissible. Since the cloths do not touch the pot as the utensil is wider than the pot, it is not considered Hatmana. Similarly, it is permitted to place a pot into our ovens by putting a raw piece into it, provided that the pot is not touching the coals. Even if the mouth of the oven is covered with cloths, since the cloths are not touching the pot it is not considered Hatmana and it is permissible. RAMA: The Hatmana which is done in these regions, whereby food is stored in the oven and the mouth of the oven is sealed with clay, is permitted according to all opinions, as explained above in Siman 254 and will be explained below at the end of Siman 259. It is a mitzvah to wrap food for Shabbos so that he will have hot food to eat on Shabbos, for this is an honor and delight of Shabbos. Whoever does not put trust in the words of the sages and forbids eating hot food on Shabbos, may be suspect of being a heretic. (Baal HaMeor Chapter 'With What Do We Insulate' etc).