This Forty Below® Bottle Boot™  is a 1-Liter insulated water bottle cover designed to help keep water from freezing, and has been extremely popular for use on extreme cold weather trips and expeditions around the world for over 40 years. This is the most popular and versatile size and shape available, since it will fit the most commonly used Nalgene® 1-Liter and 32 oz quart size water bottles. The closure uses no zippers that might break or freeze, and is designed to be opened easily while wearing mittens or gloves. Available in assorted colors.