Stainless Steel: Both the container tank and utensils of the tiffin lunch box are made of 304 stainless steel with excellent corrosion and oxidation resistance. Easy to maintain. PU foam insulating layer: High-density insulated pu foam is applied to the middle layer, which makes food stay warmer than those with vacuum layer. At room temperature this food thermos will keep warm/cold for 4 hours. 3-Layer