"Bunny boots" is the most common nickname for the Extreme Cold Vapor Barrier Boots used by the United States Armed Forces. These large waterproof rubber boots can be worn in extremely cold weather (for example hunting, snowmobiling, or ice fishing). The liner-free interior retains warmth by sandwiching up to one inch of wool and felt insulation between two vacuum-tight layers of rubber; this vacuum layer insulates the wearer's feet similar to a vacuum beverage flask.
Originally designed during the Korean War for military expeditions in extremely cold weather, the Extreme Cold Vapor Barrier (ECVB) Boots are rated from −20°F to −60°F (depending on the type) and have been sold to civilians in large numbers as military surplus.
This Type II white "Bunny boot" is an improved version from the Type I black "Mickey Mouse boot". This Type II white "Bunny boot" is designed for use in even more extreme cold weather, and is rated all the way down to −65 °F.
I bought these bunny boots new to climb Denali, but have never used them. They are nice and warm.