Big Agnes Anvil Horn 0°

The Big Agnes Anvil Horn 0° is a genuine winter bag: with a -18°C limit rating it sits in the 4-season/winter class, built for cold-weather expeditions and high-altitude trips rather than typical three-season backpacking. Insulation is 650-fill-power down treated with DownTek, which sheds moisture and blunts down's usual weak point — the collapse in loft once it gets damp. At 1328 g with 709 g of down fill, it's on the heavier side, which tracks with its temperature class; it packs to 22×15 cm. The full-length left-side zipper opens one way only, a simpler but less flexible venting setup than the two-way zips found on warmer-weather bags. An adjustable, contoured hood and the integrated Flex Pad Sleeve, which locks the bag to a pad, help eliminate drafts underneath the sleeper. Shell and liner are polyester with a DWR finish, and the materials carry bluesign certification with no PFC treatment. It's sized for users up to 182 cm and skips an internal pocket, a minor omission for a bag built primarily around winter warmth.