For hatmana, the Shulchan Aruch (Siman 257) distinguishes materials that do not add heat (eino mosif hevel) — permitted to wrap in before Shabbos — from materials that add heat (mosif hevel), forbidden even on Friday; wrapping on Shabbos itself is forbidden in every case.
The siman concludes that it is a mitzvah to insulate in order to eat hot on Shabbos, out of the honor and delight of Shabbos. For a concrete setup (cholent, pot, hotplate), ask your Rav.
Hatmana (wrapping a pot to keep it hot) turns on a central distinction: מוסיף הבל (the material adds heat) vs אינו מוסיף הבל (it only keeps heat). One may never wrap in a material that adds heat, even on Friday; one may wrap in a material that only keeps heat before Shabbos, but not on Shabbos itself. Wrapping in order to eat hot is even a mitzvah (kavod / oneg Shabbos). For your concrete case — ask your Rav.
The cholent (chamin) that stays steaming until the Shabbos morning meal is no accident: it is the subject of a whole siman of the Shulchan Aruch, Siman 257 of Hilchos Shabbos (Orach Chaim). Eight paragraphs answering a very concrete question: how, and with what, may one wrap hot food on Friday so that it stays hot on Shabbos?
What does the Shulchan Aruch say in Siman 257?
The Mechaber (Rabbi Yosef Karo) opens the siman with the general rule:
אֵין טוֹמְנִין בְּשַׁבָּת אֲפִלּוּ בְּדָבָר שֶׁאֵינוֹ מוֹסִיף הֶבֶל, אֲבָל בִּסְפֵק חֲשֵׁכָה טוֹמְנִין בּוֹ; וְאֵין טוֹמְנִין בְּדָבָר הַמּוֹסִיף הֶבֶל אֲפִלּוּ מִבְּעוֹד יוֹם.
"One does not insulate on Shabbos itself, even in a material that does not add heat — but at twilight (bein hashmashos), one may. And one does not insulate in a material that adds heat, even by day (on Friday)."
Three time regimes emerge, crossed with two categories of materials. That is the whole mechanism of the siman.
The central distinction: adding or keeping
1. מוסיף הבל — the material that adds heat
A material that generates its own heat (by fermentation, reaction or accumulation). Wrapping in it is forbidden even on Friday. Worse: if one transgressed, the dish is in principle forbidden — even after the fact (בדיעבד).
2. אינו מוסיף הבל — the material that only keeps heat
A material that only retains the existing heat of the dish. Wrapping in it is permitted before Shabbos (and at twilight), but forbidden on Shabbos itself by decree (gezeirah).
3. הטמנה vs שמירה — insulating or merely protecting
Surrounding the pot to keep the heat = hatmana. Placing a lid or an object to protect the dish (dust, animals), with no thermal aim = shemirah, permitted even on Shabbos. The criterion is the intent.
The table of materials (Seif Gimel)
The siman draws up two explicit lists:
| Category | Effect | Examples from the source |
|---|---|---|
| מוסיף הבל | Adds heat — forbidden, even on Friday | Olive or sesame pulp, manure, salt, lime, sand (wet or dry), straw, grape pomace, chaff, damp herbs |
| אינו מוסיף הבל | Only keeps heat — permitted before Shabbos | Clothing, fruits, feathers (pigeon and others), flax tow, craftsman's sawdust |
The distinguishing criterion: מוסיף הבל materials produce their own heat; the others only retain the dish's heat.
The other cases of the siman (seifim ב–ח)
| Seif | Situation | What the source says |
|---|---|---|
| ב (2) | Placing an object on the pot | To protect (mice, dust) → permitted: it is shemirah, not hatmana |
| ד (4) | Re-covering / adding / substituting the Shabbos covering | Permitted if the pot is fully cooked; forbidden if it is not fully cooked |
| ה (5) | Transferring the dish into another pot on Shabbos | One may then wrap it in a material that does not add heat — a new situation |
| ו (6) | Wrapping a cold dish | Permitted in a material that does not add heat; forbidden in a material that adds, even on Friday |
| ח (8) | Pot on a heat source + blankets | If the cloths touch the pot heated by the fire → hatmana forbidden; if they do not touch it → permitted. Mitzvah to insulate in order to eat hot (kavod / oneg) |
Sephardim and Ashkenazim: the Rema's nuances
The Rema (Rabbi Moshe Isserles) brings several leniencies reported in the siman: if one forgot and inadvertently wrapped (shogeg) in a material that adds heat, one may eat the dish; and some permit wrapping on Friday in such a material when it is for the next morning (and not for the night), without making it a habit. Customs differ between communities — hence the importance of knowing your own minhag.
Modern application: cholent, insulated pot, blankets
Now we see why this siman speaks directly of our Shabbos kitchens:
- The wrapped cholent? It is the classic case of hatmana — and the siman recalls that keeping a dish hot for Shabbos is a mitzvah.
- A towel, an ordinary blanket, aluminum foil? They keep the heat (אינו מוסיף הבל): one wraps before Shabbos, not during it.
- A heating blanket or a source that warms the blanket? One shifts to מוסיף הבל, with all the stringency of the siman.
- The insulated pot and the hotplate? They cross hatmana with the shehiyah rules of Siman 253 — hence real practical details to check.
Several contemporary authorities rely on this framework to discuss modern setups — with nuances depending on the minhag, the material and the contact (or not) with the heat source.
This article presents what the source says for the purpose of study. It does not rule on any practical case. To know whether your setup — cholent, insulated pot, blankets, hotplate — is permitted according to your community, ask your Rav.
Frequently asked questions
What is hatmana?
It is surrounding a pot with a material to maintain or increase its heat for Shabbos. Siman 257 distinguishes it from mere protection (shemirah) — placing a lid or an object with no thermal aim — which remains permitted even on Shabbos. The criterion is the intent. For a concrete case, ask your Rav.
What is the difference between מוסיף הבל and אינו מוסיף הבל?
The first adds heat of its own (pulp, salt, lime, sand, manure): forbidden even on Friday. The second only keeps the heat (clothing, feathers, tow): permitted before Shabbos, forbidden on Shabbos itself.
May you prepare an insulated cholent for Shabbos?
The siman concludes that it is a mitzvah to insulate in order to eat hot (kavod / oneg Shabbos). The hatmana must be done before the onset of Shabbos and respect the distinction of materials, not to mention the details of modern warmers. For your setup, ask your Rav.
Study Siman 257 in depth
Four levels, from beginner to talmid chacham — Hebrew text, translation, pilpul and the shitah of the Admur HaZaken.