The Crispi Wild Rock Plus GTX is fully insulated boot with 800 grams of Gore Duratherm XL Kelvin insulation all the way around the boot. This is the warmest boot that Crispi makes. It features a full grain leather and tread pattern designed to deal with and shed water, mud and all of the nasty elements you'd see in the high mountains during late fall and winter months. Flex Rating: 3