The Ultralight Sleeping Bag from L.L.Bean is the first to use a new insulation called PrimaLoft Gold with Cross-Core, which uses a combination of traditional fibers and Aerogel to keep you warm. Originally developed by NASA, aerogel is a super lightweight insulator with an incredible weight to warmth ratio. It’s being integrated into outerwear and winter footwear by lots of brands but now Bean has taken it a step further.