This warm boot has kept hunters toasty for over a decade with a 5mm CR Flex-Foam fleece liner with the added 2mm thermal foam under foot. It's a proven combination at frigid temperatures embraced by hunters on the stand and in the blindSpecial Sizing Note:Muck boots are unisex sizing and in whole sizes only. These boots should be chosen based off of athletic footwear sizing and best fit is achieved by wearing a midweight sock. When using heavyweight socks, true half sizes should select the next size up. Muck boots can be worn with Orthotics and molded sock liners. Please see the sizing chart below for fit information. FeaturesWarm fleece lining2mm thermal foam under the footbed5mm CR Flex-FoamEVA contoured molded midsoleMS-1 molded outsoleComfort topline