Generally, the qualified insulation bottle inner layer on the market is made of 304 and 316 materials. 201 stainless steel outer layer is also qualified.
About the insulation bottle inner layer：
316 stainless steel is better than 304 stainless steel when economy allows.
316 stainless steel is a medical grade material, and its safety and hygienic performance will be more prominent than 304 stainless steel. It can be used for milk, coffee and tea; Its hygienic performance is that it is not so easy to breed bacteria.
304 stainless steel is the material used to produce insulation bottle according to the national standard. Most insulation bottle on the market are made of 304 stainless steel, which is relatively affordable. The inner layer of 304 stainless steel insulated bottle is not afraid of tea and coffee, but generally the durability of 304 stainless steel is not as strong as that of 316 stainless steel.
In terms of thermal insulation performance, the insulation bottle of 316 stainless steel inner layer will be better.
About the insulation bottle outer layer：
The outer layer does not directly contact the water in the bottle, and the material of the outer layer is not specially specified.
The outer layer of the common thermal insulation bottle on the market is made of 201 and 304 stainless steel. Although 201 stainless steel is forbidden to be used as the inner layer of the insulation bottle, the material used as the outer layer is allowed.
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