Hot Chillys La Montaña is our king of the mountain for warmth. The fabric of these men's thermal pants consists of brushed, micro-denier polyester fleece for lighter weight and greater strength and durability. Hot Chillys two tone microfiber waistband with plush-back ME Chamois gusset Horizontal fly construction Micro-denier polyester fibers for lighter weight, luxurious drape, breath-ability,  strength and durability MTF polyester moisture transfer fibers for increased moisture management UPF 40 protection Mountain weight, active fit