There is no harm in copper plating the 316 stainless steel liner. 316 stainless steel is not harmful to our body. It can withstand high temperatures from 1200 degrees to 1300 degrees. It is also extremely corrosion-resistant and does not dissolve harmful substances inside. It is often used to make medical equipment and infant items. Copper plating on the inner tank is not harmful to the human body. In the past, most water cups were silver-plated, but now most thermos cups use a copper-plated inner tank design, which makes the thermos cup have a better heat preservation effect.