Big Agnes Greystone 0°

The Big Agnes Greystone 0° is a mummy-shaped winter down bag built for expedition-style trips and cold multi-day tours where temperatures drop well below freezing. It uses 952 g of 600-fill DownTek hydrophobic down, and at a total weight of 1502 g that works out to 93.9 g per degree of warmth — a solid, if not class-leading, warmth-to-weight figure. Comfort and limit ratings of -9 °C and -16 °C come from EN 13537 testing, so the numbers are directly comparable across brands. Both shell and liner are recycled polyester, the down carries RDS certification, and the whole bag is bluesign-approved and PFC-free, which matters to buyers who weigh sourcing alongside performance. An insulated draft collar and full-length draft tube along the two-way zipper cut heat loss at the seams, while the zipper lets you vent from either end. At over 1.5 kg this is not an ultralight piece of kit — it is a dependable foundation for winter camping and shoulder-season trips where warmth and durability outweigh pack weight.