Western Mountaineering UltraLite

The UltraLite is Western Mountaineering's benchmark three-season mummy bag: 850+ fill-power goose down, rated to 20°F (-7°C), hand-sewn in the USA from 12D nylon ripstop with a DWR finish. At 820 g (Regular) with 455 g of fill, it delivers a warmth-to-weight ratio well above the brand's summer-weight bags, reflecting the mummy cut's thermal efficiency over the roomier semi-rectangular and rectangular models in the range. Details support the cold-weather rating: an insulated draft collar in addition to the zipper draft tube, a fitted contoured hood, and coupling compatibility with a second bag. The single-direction, left-side zipper is a small weight-saving trade-off compared to two-way models elsewhere in the lineup. This is a well-established reference point in ultralight three-season sleep systems — light enough for thru-hiking base-weight goals, warm enough for shoulder-season nights down to around -7°C, without the added bulk of dedicated winter bags. The trade-off is the narrower mummy cut, which suits back and side sleepers who don't need extra shoulder room.