Sierra Designs Backcountry Bed SYN 2.545;Season Sleeping Bag Zipperless design - no hardware, cords or Velcro to get in the way of your comfort. Catenary shaped opening is smaller than bag width, so when you push out, the walls push in to seal out drafts. Versatile integrated comforter wraps naturally to your preferred sleeping position, and easily adjusts to varying temperatures. Insulated hand/arm pockets provide warmth when the comforter is outside of the bag. Sleeping pad sleeve secures your pad to create a fully integrated sleep system.