Bamboo Stainless Steel Thermo Flasks are water sustainably and guilt-free. Insulated with a stainless steel inner wall to keep the drink warm and a hand screw top lid, this eco-friendly flask is ready for you to take home. Bamboo Stainless Steel Thermo Flasks come with a metal tea infuser that is ideal for brewing loose leaf tea. It is usually made out of layers of stainless steel that help reduce heat transfer. It also contains layers of stainless steel and bamboo material that further reduce heat transfer.