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Western Mountaineering says:
Known by Volcanologists the world over you’d think this Puma MF was filled with high lofting lava! 9.5″ of loft, 36 oz. of 850+ fill power down, two densely packed Interlocking Draft Tubes and a full down filled collar will keep you in the ring of fire till 25 below zero. Its VBlock Side Baffle provides phenomenal down control, so necessary in a bag with this much loft. You get a 64″ shoulder girth so that there’s even room for layering. The MicroLite XP™ shell has superior breathability while being extremely water resistant. This bundle of warmth weighs in at just 3 lb. 7 oz. total weight.
Rating & Materials
* Western Mountaineering state: 'We independently verify own temperature ratings through our own testing, customer feedback and design knowledge. Most of the items in our catalog we have been making for years, which means we have lots of prior knowledge from everyday consumers on what ratings are accurate. We have also EN tested our bags. In every case the EN rating is lower than our posted rating. This means our ratings are more conservative. We do this to ensure that almost everyone will be happy in our bags at the temperature we publish.'