Tested in the frigid winters of LaCrosse, Wisconsin, Pac boot replacement liner is built with insulating foam. Not only does the liner add warmth to the boot, but it adds an extra layer of cushioning for long-wearing comfort. LaCrosse lightweight 9mm foam adds insulation and cushioning to any Pac boot. The open cell construction allows for better air circulation keeping you dry and comfortable. Material: Polyester, Foam.