Western Mountaineering MegaLite

The Western Mountaineering MegaLite is a 3-season mummy bag with an EN ISO 23537 lab-tested rating — comfort 0°C, limit -6°C — rather than a manufacturer estimate, which makes its numbers directly comparable across brands. It weighs 680 g in regular size, filled with 340 g of 850 fill-power goose down inside a 12D ExtremeLite ripstop shell with a 12D taffeta liner, and packs to 33×18 cm (6.6 L). Continuous horizontal baffles keep the down from shifting, a draft collar and draft tube block heat loss at the neck and zipper, and the fitted, adjustable hood cinches down around the head. The shell carries no water-resistant treatment, so it depends on a dry tent or bivy rather than damp-ground resilience. At roughly 113 g per degree of warmth, it is not the most thermally efficient bag in the lineup, but 680 g for a true 0°C-comfort mummy bag is competitive for three-season backpacking and thru-hiking, where shoulder-season nights can still dip toward freezing. Regular sizing fits users up to 183 cm.