Swistech's thermos cup is made with double wall insulation with copper lining for maximum insulation. The liquid can keep the heat for 6 hours and the cold for 18 hours. The design of the thermos cup is provided with a handle that, in addition to giving you a good grip, can also be used to tie the cup to your backpack. The cups are made of non-reactive and lightweight 18/8 stainless steel which has higher corrosion and oxidation resistance than regular steel, this prevents odors and is easy to clean. They are also BPA-free.