Lightweight and amazingly comfortable, the Super Stretch Burrow Bag #4 features Montbell's patented Super Stretch System and Exceloft synthetic insulation. This is the bag for you if you are going to constantly be in a wet environment and want the added security of a synthetic bag. Exceloft synthetic insulation absorbs less than 3 percent of water when wet, therefore keeping you warmer when your bag gets wet. Uses lightweight, durable, high-density nylon taffeta.