The KENETREK 6mm 13 inch LINERS are quilted from three seperate materials. A durable synthetic material on the inside wicks away perspiration. 400 grams of Thinuslate Insulation keeps you warm without the bulk of traditional felt liners. Finally, 3mm of quality wool felt holds moisture away from your skin and continues to insulate even when damp. We recommend purchasing an extra set of these liners with your boots to rotate them daily, assuring you of always having dry comfortable boots to put on in the morning.