Big Agnes Star Fire UL 20°

The Star Fire UL 20° is an ultralight mummy bag from Big Agnes's flagship UL line, built for the best possible warmth-to-weight ratio. The fill is 850-fill hydrophobic DownTek down — among the highest available down grades — enclosed in a Pertex Quantum shell, an extremely light yet durable, DWR-treated fabric. EN ISO 23537-tested ratings put comfort at -2°C, the limit at -8°C, and extreme at -27°C, making it more of a cold-shoulder-season bag than a pure summer piece. At 879 g and a weight-per-degree figure of just 109.9 g, it is among the most efficient bags in its class — vertical continuous baffles keep the down evenly distributed and stop it shifting to the underside of the bag over time. A half-length zipper on the left side saves further weight versus a full-length zip, at the cost of somewhat less venting flexibility. A draft collar combined with a draft tube along the zipper limits heat loss. It is a strong choice for thru-hiking and lightweight multi-day treks where every gram counts, at some expense of comfort in warmer conditions.