Because tinplate has the lowest cost, you may ask why not make it like coke cans or stainless steel? Because the cost of coke cans is very high, an aluminum can now costs 80 cents (many people think it is only worth one or two cents, but it is not), and if it is made into a large can, the overall hardness is not enough, and the grade of plastic is not enough, so the extrusion bearing capacity of plastic during transportation can not meet the requirements; Stainless steel is more expensive, so choosing low-cost tinplate is the best choice, so eight-treasure porridge and canned fish are made of relatively cheap iron.