The Big Agnes Bolten SL 20 Degree Sleeping Bag is a superlight sleeping bag for backpacking adventures. Technical prowess comes in the form of a mummy shaped bag, filled with PrimaLoft; Silver and Gold Insulation Active. The combination nylon rip-stop and Polyester Spandex stretch fabric shell not only keeps the Insulation in check, but allows you to move in your sleep. Talk about a shining star for all the side sleepers out there. Traditional mummy shape but with stretch side panels and Primaloft Gold Active Insulation for increased range of motion Insulated stretch side wall panels allow for great Fit and more mobility than traditional mummy bag Fit Stretch Insulation moves with the fabric eliminating loss of CLO value (Insulation properties) when stretched Stretch fabric and Insulation in key Areas maintain Insulation properties, increase mobility, and decrease bag weight Trim Fit mummy shape keeps these bags lightweight and increases thermal value Vaulted foot box creates more wiggle room for your feet Easy access top zipper Primaloft Silver insulates the core Areas of the bag on top and bottom Primaloft Gold Active insulates the side stretch panels Low profile cord lock lets you un-cinch the hood with one hand Anti-snag draft tube is soft and prevents heat loss along the zipper Zipper Garage Interior fabric loops for sleeping bag liners Exterior loops for hang drying or storage Mesh storage sack and nylon stuff sack Nylon rip-stop shell fabric with a water repellent finish Polyester Taffeta lining Partial quilted construction PrimaLoft Silver and PrimaLoff Gold Active