Thermal Protection Guaranteed The Radiantex Replacement Boot Liner offers triple protection against extreme cold with the most innovative thermal technology. Each liner has three layers: Radiantex aluminum on the exterior to reflect the cold, a layer of blended wool felt that insulates and locks in moisture, and a polypropylene inner lining to wick moisture away from the foot. Reinforced with Naugahyde heels, the Radiantex Replacement Boot Liners are resilient insulators. You'll never want to leave the house without them. Please note that this replacement liner is sized for boots with existing removable liners and may not fit boots with permanent lining. Liners are unisex and do not come with a left or right foot orientation. The felt will compress and conform to feet over time ensuring a comfortable fit. Please see our sizing specifications to ensure the right fit for your boot. To use our sizing guidelines: 1. Place your feet flat on a piece of paper and mark your longest toe and the back of your foot. It's best to do this standing and wearing winter socks. 2. Measure the length (cm) straight from your longest toe to the back of your foot using a ruler or measuring tape. 3. Use the chart to find your size.