First, buy through formal channels and try to choose products from well-known brands. When purchasing, consumers should pay attention to checking whether the instructions, labels, and product certificates are complete, and avoid buying "three no products".
Second, check whether the product is marked with its material type and material composition, such as austenitic SUS304 stainless steel, SUS316 stainless steel, or "stainless steel 06Cr19Ni10".
Third, open the vacuum flask and smell it. If it is a qualified product, because the materials used are all food grade, generally there will be no peculiar smell.
Fourth, touch the mouth of the cup and the liner with your hands. The liner of the qualified thermos cup is relatively smooth, while the inferior thermos cup mostly feels rough due to material problems.