Outerwear and apparel giant Patagonia is getting into sleeping bags. GearJunkie saw the first sample this week.

The Hybrid Sleeping Bag comes to market in September. With it Patagonia tries for a new kind of sleeping system that only insulates the lower half of the body, relying on a piece of shell material (and a worn jacket/parka) for insulation on the upper half.

The bag weighs a scant 1 pound yet can provide enough warmth for winter ascents. The design is adaptable, usable through different seasons depending on the outerwear a climber brings.

Stuffed with 850-fill down, the bag’s temp rating depends on the jacket worn with it. The system we saw used a new Patagonia alpine model, the Grade VII Belay Parka, and the sleeping bag was set for about a 10-degree rating, a company representative told us.

You must wear a winter parka on top and sleep in the parka. The top of the bag is made of thin shell material (see details below).

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The system is meant for serious mountaineers and backcountry enthusiasts who will inevitably bring an insulating parka during an outing. The wear-your-jacket-to-bed theme eliminates redundant gear when climbers are trying to go as fast and light as possible on a peak.

Patagonia Sleeping Bag

Called an “elephant foot” design, the bag puts insulation only in the bottom half of the baffled body. The top is a thin fabric, the company’s windproof Houdini material, which is a 1.2-oz, 15-denier, rip-stop nylon with a DWR (durable water repellent) finish.

The bottom of the bag is more traditional, using Pertex Quantum shell fabric made of .85-oz, 15-denier nylon.

A half-length zipper saves weight, and draw-cords atop the insulated portion and at the hood help seal in warmth, Patagonia notes.

As noted above, its minimalist build makes for an approximate 1-pound weight for the bag. It packs small, about the size of a football, for easy transport on a mountain.

–The Hybrid Sleeping Bag will cost $299 when it comes to market the first week of September. It will be for sale at Patagonia.com and in Patagonia retail stores.