On the inside of the jacket there are buttons for attaching the insulating liner in cold weather. The liner is specified by MIL-L-43536. It has open underarms, buttonholes at the neck and front edges, and buttonhole tabs at the sleeve bottoms for attaching the liner to the jacket. The liner is quilted and made of polyester batting covered with 3 plies of ripstop nylon cloth. It was redesigned (i.e. buttons were added to its front) to make it capable of being worn independently of the field jacket.