Is there a problem of hatmana on Shabbos if I completely cover my kugel (taken from the fridge) or challah with tin foil on my blech or on top of my chulent pot? Is there a difference between using a few layers of foil or just one layer?
Placing food that is completely covered near a heat source will be hatmana bdavar hamosf hevel and is has a hatmana issue, however if there is a covering over it for protection reasons, i.e. a pot cover used to prevent things from falling on to it, then it is permitted. Therefore, if one layer of silverfoil is on it, for protection, i.e. to keep in the foods moisture, then it would be permitted, however a number of layer is obviously there to add to the heat, and that would not be permitted.
Machazeh Eliyahu 32-3, The Halachos Of Shabbos (R’ Eider zt”l) ftnt. 1198, V’dibarto Bom 1-65 (1), The Shabbos Kitchen chap. 6 ftnt. 2, Minchas Shlomo 2-34(7), Shmiras Shabbos Khilchoso 1 ftnt. 254.