Thermarest Altair 0 Down Bag Sleep Securely: Synergy Link Connectors bring your sleeping bag and mattress together for uninterrupted sleep Sleep Warmer: Zoned Insulation puts fill where you need it most, for efficient warmth Move Freely: Our Efficient Comfort design gives you room to move where you need it, without creating too much space to heat efficiently Carry Less: Lightweight, 750+ fill goose down offers compressible warmth