The coating of the inner container of the coppersmith's thick kettle contains copper, which has good heat conduction effect. The inner layer of the liner is alloy, but the liner can't be all copper, which can't meet the food-grade standard. Aluminum has uniform heat conduction, easy molding and beautiful appearance, and can be compounded with other metals or alloys. It is the main material of mid-range cookware. However, in the actual use process, the aluminum liner can not directly contact with food, and the surface must be protected. The aluminum liner also looks thicker.