Tiger Chef 32 Quart Aluminum Steamer Insert Basket for Stock Pot Steam, Boil, Fry Accessory Basket Stainless steel with a Heavy-Duty 3-ply bottom consisting of two layers of stainless steel surrounding a 5 mm thick aluminum core. This affects even heat distribution spreading heat quickly and evenly, eliminating hot spots. Mirror polished stock pot in stainless steel comes out beautifully of the dishwasher looking like new. NSF means a HIGH QUALITY. Items marked with the NSF logo means that the item and its manufacturing facility was tested and approved by the independent testing company called NSF to be safe for commercial use.