Cumulus Alaska 900

The Cumulus Alaska 900 is a full-size winter expedition sleeping bag built for genuinely cold conditions, not shoulder-season use. Its 900 g fill of white duck down at 700 fill power (US standard, 95/5 down-to-feather ratio) sits in a dual H-baffle system that layers two chambers to reduce cold spots where stitching would otherwise compress the insulation. That gives it a manufacturer-rated comfort temperature of -10 °C, a limit of -18 °C, and an extreme rating of -39 °C — figures aimed squarely at winter expeditions and sub-zero bivouacs, not general 3-season backpacking. At 1400 g total weight with a Pertex Quantum 35 g/m² DWR-treated shell, the bag trades ultralight ambitions for genuine cold-weather capability: a two-way zipper, 3D anatomical hood, anatomical foot box and draft collar all add function and weight simultaneously. It's also coupleable with a matching bag. For anyone hiking in temperatures much above freezing, the Alaska 900 is overkill — its value is specifically in extreme cold where lighter bags simply aren't warm enough.