Aerogel weighs almost nothing, yet is an outstanding insulator. Which makes it perfect for the L.L.Bean Ultralight Sleeping Bag. This mummy-style bag is filled with a new insulation called PrimaLoft Gold with Cross-Core, which combines aerogel with other fiber technologies. As a result, the bag weighs under two pounds and packs down to just 14" x 6.5", yet retains much of its insulating ability even when compressed. Available in regular or long versions.