It's a shame you have to trek with a heavier backpack when you're trekking in freezing temperatures--winter attire is much heavier than summer--but at least the Therm-a-rest Oberon Sleeping Bag packs down to the size of larger water bottles. Its 800-fill down insulation is ridiculously lofty, compressible, and surprisingly light for how warm the bag feels. The down is treated with Nikwax for hydrophobic properties that keep the down lofty and warm in moisture-riddled environments. Therm-a-rest lined the bag in ThermaCapture to reflect your body heat back to you for a boost of warmth. You'd think this lightweight bag wouldn't come with any additional features, but the Oberon has sleeping pad connectors and blanket loops for fully-featured convenience.