Sleeping Bag Product

Overview

A sleeping bag is a portable insulation system. It does not generate heat; it slows the rate at which a sleeping body loses heat to the night air by trapping a thick layer of still air around the sleeper. In this bag that air is held in the loft of 450 g of goose down inside the Insulation System, sandwiched between an outer Outer Shell and an inner Inner Liner. The mummy cut tapers from 157 cm at the shoulders to 99 cm at the foot, minimising the volume of air the body has to warm.

The bag is rated to ISO 23537: a comfort temperature of −1 °C, a lower limit of −7 °C, and an extreme survival rating of −24 °C. The ratings come from a heated manikin test, not field opinion, which makes bags from different makers directly comparable.

Shell and liner

The Shell Fabric (20D Ripstop) is 20-denier nylon ripstop at about 38 g/m², calendered (heat-pressed) so the weave is tight enough that down clusters cannot work through it. A PFC-free durable water repellent makes condensation drips bead off rather than soak in. The Liner Fabric (15D Taffeta) is a softer 15-denier taffeta chosen for skin contact.

The two envelopes are not the same size. The liner is cut smaller than the shell — a differential cut — so a knee or elbow pressed against the inside pushes the liner, not the insulation, and the down between the two layers keeps its loft. Sewing uses fine bonded Seam Thread so needle holes stay downproof. A Stash Pocket inside the chest keeps a phone battery warm, and Pad Attachment Loop anchors stop the bag sliding off the sleeping pad.

Insulation

Down insulates by lofting: each cluster springs into a three-dimensional plume that immobilises air. The 800-fill-power rating means 28 g of this down lofts to 800 cubic inches, so a small fill weight produces a thick insulating layer. To keep that fill where it is needed, the space between shell and liner is divided into chambers by mesh Baffle Wall strips — box baffles, which unlike sewn-through quilting leave no stitch lines where the insulation thickness drops to zero. Each chamber is blown full of a weighed charge of down and closed with a Fill Port Closure. The Footbox Chamber carries about 20% extra fill because feet have poor circulation and press the bag against the ground.

Zipper, hood, and draft control

A bag is only as warm as its leaks. The Zipper System uses a 160 cm YKK #5 coil Main Zipper (YKK #5 Coil) with two opposed Zipper Slider units, so the foot end can be opened for venting on mild nights while the torso stays sealed. A stiffened Anti-Snag Strip keeps the light shell fabric out of the slider jaws. Behind the full zipper length hangs the Draft Tube, a down-filled tube that covers the cold line the coil would otherwise put against the sleeper's back. At the top, a Zipper Garage hides the metal slider and a Hook-and-Loop Tab keeps the zip closed if the slider lock creeps.

The head can dump a large share of total heat loss, so the Hood Assembly is a shaped three-panel cup with its own Hood Down Chambers chambers. Its Hood Drawcord cinches the face aperture down to breathing size; sleepers should breathe outside the bag, because exhaled moisture condensing in the down collapses its loft. The Draft Collar is a separate down-filled horseshoe at shoulder height with its own Collar Drawcord. Sealed around the neck, it stops the bellows effect — warm air pumped out of the bag every time the sleeper rolls over — which on a cold night matters as much as fill weight.

Packing and care

For transport, the bag stuffs (foot first, never rolled) into the Compression Sack; four Compression Strap and Strap Ladderlock sets pull it to roughly 8 litres, an 18 × 33 cm cylinder. Compression is safe for days, not months: stored crushed, down clusters take a permanent set and lose loft. At home the bag lives loose in the 30-litre Storage Mesh Sack.

Washing uses a down-specific detergent in a front-loading machine, followed by a long low-heat tumble with dryer balls to break up clumps. Ordinary detergents strip the natural oils that let clusters spring back. With this care a quality down bag holds its rating for well over a decade — far longer than synthetic fills, which lose loft each time they are packed.