quilted pot cover; insulated pot cozy
A thick, often quilted cover placed over a pot or pan to retain heat after cooking, commonly used in energy-saving cooking methods.
If you use a pot cozy, the food stays warm even after you turn off the heat.
Compound of 鍋 (nabe, 'pot') and 帽子 (bōshi, 'hat'), from its hat-like shape and function of covering a pot.