The Slick Rock uses a Primaloft insulation. This is our lightest and most compressible synthetic insulation mummy bag. This fill absorbs less water and is warmer wet or dry. The 2-layer offset construction gives you a warm bag rated at 20 or 0 degrees. A contoured hood, a self repairing #8 YKK zipper, and a 300T round ripstop outer give you the features you need in a good backpacking mummy bag. A compression stuff sack is included. 42% more compressible than continuous filament bags (per Primaloft technical information).