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For optimum insulation with least weight and bulk, a sleeping bag should be made utilizing the offset-seam principle, with a continuous layer of 100 per cent pure down surrounding the sleeper. The best design will also incorporate the differential cut which allows the inner shell to be stretched at points of contact without tightening the outer shell, thus diminishing the thickness of the insulation. Zippers, if any, should be protected with down strips. The outer cover should be water-repellent, not waterproof. The mummy design is best with hood arrangement that can be either fully open or tightly closed. With a bag designed to conserve heat most efficiently, with bags placed close together and with most of the skier's daytime clothing worn in the bag,to 3 pounds of down will be adequate down to —30° F. Such a bag will weigh from 4 to 6 pounds. Multiple sleeping bags, holding 2 to 3 people, conserve heat most efficiently and save weight and space. It is important to prevent heat loss through to the snow layer beneath. While air mat- |
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