Containers: The set usually includes three or four individual containers. High-quality versions feature 304 stainless steel interiors for food safety and durability, and many are leakproof with silicone sealing rings.Insulated Bag: The accompanying "Lunch box bag" is lined with thermal material (such as Oxford cloth or canvas with an aluminum layer) to help preserve heat or cold.Portability: Containers often feature hidden handles or stackable designs to save space.