The Snugpak Expansion 3 is a great choice for winter outdoor adventure with a high temperature rating. The 3 season bag has a extra wide built in expansion panel in the zipper that allows the bag to increase in width for more comfort while warmth is maintained. The Softie® Insulation which was developed uniquely by Snugpak uses super fine synthetic yarns bound with special resins which creates a true down like feel for the user. The staple yarns minic the compositions of natural insulation Snugpak Softie Expansion 3 Sleeping Bag | Synthetic Sleeping Bag | George Fisher