At 240 g total weight, the Cumulus Magic 100 Zip is the lightest bag in this Cumulus range — built purely for summer bivouacs and warm-night ultralight trips where every gram in the base weight matters. Just 105 g of 900-fill-power goose down (a notably high fill power, at a 98/2 down ratio) is enough to earn a manufacturer-rated comfort of 13 °C and limit of 10 °C, reflecting how little margin this bag carries for anything below mild summer temperatures.
Horizontal H-baffles keep the sparse down fill from shifting, and the full-length two-way zip runs down the left side. Packed size is just 18 × 11 cm at 1.6 litres — small enough to fit in a hip belt pocket on some packs. Internal length is 182 cm, shoulder width 75 cm, hip width 47 cm, so it suits shorter and more compact users best. This is a specialist bag: excellent for warm-weather minimalism, but with no meaningful cushion against a cold snap.