Western Mountaineering Materials

850 Plus Fill Power Goose Down
Western Mountaineering has always used the highest fill power goose down available. Once it has been conditioned, this natural fiber provides a better warmth to weight ratio than any other material. Down clusters exhibit unique branching structures that create tiny pockets of dead air, trapping and holding your body's heat. Thanks to this high tech marvel of natural engineering, a down filled sleeping bag is as much as 35% lighter than it's synthetic counterparts and lasts 3-5 times as long! It is more compressible than synthetic insulation and provides the most warmth with the least bulk. High fill power is the only way Western is able to achieve such aggressive temperature ratings from such lightweight bags. They send each batch of down to an independent laboratory for testing and each batch must meet a mimimum of 850 fill power. The higher the fill power the more warmth per ounce of down, so a high fill power bag is feather light and toasty warm.  

Fabrics
Western uses three main fabrics: ExtremeLite, Microlite XP, and Gore Windstopper:

The ExtremeLite shell fabric is a tightly woven ripstop nylon with an extremely high thread count. This creates a surprisingly strong, down proof material that still comes in at under 1 oz. per square yard. Although some durability is sacrificed with these lighter fabrics, the ExtremeLite bags are perfect for the lightweight specialist.

MicroLite XP employs a dense weave of ultra fine yarns to achieve "the ultimate balance of breathability and water resistance". At 1.3 oz. per square yard it's still more lightweight than most shell fabrics, but for a breathable material it boasts truly impressive water resistance. It's a versatile fabric that allows you more flexibility when conditions turn sour.

Gore Windstopper is a well known material and a trusted brand name. You can expect the same GoreTex performance that we've all come to depend on. It's the most weather resistant fabric used by Western, and it provides the ultimate protection. The waterproof breathable membrane allows water vapor out while keeping raindrops from coming in, sealing you off from the elements. Windstopper is used in damp or extreme conditions. Some winter conditions may require the use of the Hot Sac Vapor Barrier Liner for maximum performance. (See VBL)

Internal baffles are contructed from a lightweight no-see-um netting that is highly breathable and somewhat stiff. This helps reduce distortion and allows the bag loft up more quickly with the added benefit of easy compressibility. 

The two expedition Windstopper bags (Puma and Bison) both use an abrasion resistant taffeta in the footbox. The heavier fabric is a welcome addition if you plan on storing boot liners or cold sensitive equipment in the foot of your bag. 

Zippers
Full length YKK# 5 zippers are used on all Western bags with the exception of the Highlight (one-way, half length, YKK# 4 1/2). The fact that all of their bags share a common zipper makes it easy to zip them together and create a double bag. Just be sure to get one bag in right zip and one bag in left zip so that they match up. (see "Summer Coupler")

Water Repellent Treatments
All Western Mountaineering fabrics are treated with a DWR (Durable Water Repellent) coating. It's an 80/20 DWR, which means it will keep 80% of the coating after 20 washes. Western is clear to point out that this is a laboratory test, so it's not realistic for home washing. The dirt picked up in the field and abrasion from use will degrade the DWR treatment, so you'll need to re-treat the bag with DWR when water stops beading off and starts soaking though the fabric...usually after a few seasons of use.