Not many ultralight backpackers expect cutting-edge gear from the likes of larger brands like REI, but REI has been quietly producing some of the most affordable premium-quality down bags and quilts available with its Magma line. The bags use ultralight fabrics and high fill power down to achieve a high warmth-to-weight ratio without costing an arm and a leg. The REI Magma Sleeping Bag comes in 15 and 30 deg F models.