All ThermoFlask bottles are made of food-grade 18/8 stainless steel and feature a durable powder-coated finish. The lids are made of BPA-Free plastic (PP#5) and feature silicone o-rings to create a leak-proof seal.
Stainless steel contains chromium which, when exposed to oxygen in the atmosphere forms a thin invisible layer called chromium oxide. This invisible layer gives stainless steel its ability to resist stains and rust. If this layer is damaged, rust is formed on the surface at the point of that damage.
Avoid damaging the chromium oxide layer by avoiding the use of cleaners that contain chlorides (fluorine, chlorine, bromine, iodine, etc.).
Cleaners containing alcohol, ammonia or mineral spirits can also damage the protective layer. Do not use steel wool or steel brushes as minute particles of these carbon steel articles may adhere to the stainless steel and begin to rust.
Removal of oxidized stains and even “surface rust” can be done by using a paste made from baking soda and water or a cleanser that contains oxalic acid, such as Bar Keeper's Friend Soft Cleanser. If using baking soda and water, use a cloth or soft bristle brush, and rub the baking soda in the direction of the grain. This may take a little effort, but this will remove these soils.
Do not use in microwave or freezer. Do not use on stove for cooking Allow hot liquids to cool to a drinkable temperature prior to sealing lid. Do not overfill product. Hot liquids can scald you. Keep out of reach of children when filled with hot liquids.