The unique ability to swap in a fresh liner for dryness and comfort. It's part of what makes our Pac boots so trustworthy in the most extreme conditions. This three-part quilted liner is made from Cambrelle, 400-gram Ultra Thinsulate Insulation, and wool felt, creating a liner that wicks perspiration, provides warmth without bulk, and is more durable than standard felt liners. Fits our Montana boots.