May one insulate food before Shabbat with a substance that adds heat (mosif hevel)?

ShabbatCooking

Synopsis

The Mechaber prohibits insulating with a heat-adding substance even before Shabbat (mi-b'od yom). The Rema records two leniencies: (1) if one forgot and insulated accidentally, the food is permitted to eat; (2) if insulating for the next day's meal (not the night meal), it is permitted before Shabbat, but only b'dieved and not as a regular practice.

Early Acharonim
Late Acharonim
Lenient
Strict
Lesser cited
Major authority

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