Like MontBell's existing Super Stretch System, their new Super Spiral Stretch System is unique. Basically MontBell found an alternative way to create a stretchy sleeping bag, and save some weight to boot. The technology is best described in their own words: "New for 2009, MontBell has incorporated a classic tailor's technique to address sleeping bag comfort issues. By integrating a woven fabric "cut on the bias" and orienting the fabric's warp and weft threads at 45 degrees to major seam lines the sleeping bag becomes more fluid or elastic in nature. Additionally, "spring like" crimped fibers are used in the weave of the fabric to capitalize on their inherent stretch properties." Rather than the traditional horizontal or vertical orientation of the down tubes, they are oriented on a 45 degree angle, and appear to spiral around the sleeping bag.
The new Spiral Down Hugger line also introduces MontBell's new 12 denier Ballistic Airlight sleeping bag fabric. Switching from 15 to 12 denier fabric plus spiral construction reduces the weight of a sleeping bag by about 2 ounces. Apparently MontBell is very satisfied with the new technologies because they intend to extend the Super Spiral Stretch System across their entire sleeping bag line (available March 2010), replacing the current Super Stretch technology.
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