Thermarest Navis 25 Degree45;45 Degree Sleeping Bag System-Oriented: Hybrid Construction works with your insulated jacket to reduce overall weight and bulk Secure Attachment: Synergy Link Connectors provide more benefit from your mattress Versatile: Combine the Navis with any insulated jacket for a Variable Temperature Rating Carry Less: Lightweight, 750+ fill goose down offers compressible warmth