Proof is a modern drinkware brand with a conscience. The materials Proof make their products in are superior to all others in the market. Their stainless steel is 316 medical grade, compared to the competitions 304 stainless steel. This 316 medical grade steel means there won't be any corrosion or odours. Proof also refrain from using a copper insulation layer. This may provide 1 or 2 hours extra insulation for your drink, but the waste from making this copper layer is very harmful to the environment. Proof cares about sustainability and how our products effect the human race. Prevent the use of plastic bottles and carry your drinks in a mightily fine looking and durable bottle.