Gray Wool Felt Insoles are 13mm (1/2") thick. Makes any boot warmer and replaces synthetic insoles or adds extra warmth with an existing liner. These insoles go in the bottom of your boot beneath your foot and are made of real wool felt. Liners can be trimmed to size, if needed. If you want to add warmth to your LL Bean type unlined hunting boots or rain boots use our 8mm yellow insoles.