The REI Co-Op Magma 15 falls on the top 10 list for best sleeping bags. If you are looking for a cold temperature rating sleep sack that also has a high comfort rating, this product will not disappoint. Intended for active campers, the REI Co-Op Magma is constructed for lower limit temperatures, as well as high adventure hikers who need a low weight ratio sleeping bag.\r\nWhy We Like It - Rei Co-Op Magma 15\r\nThe REI Co-Op Magma 15 is a well-constructed sleeping bag with a low limit rating that is intended to withstand cold temperatures. It is ultra-lightweight, which is ideal for high adventure hikers, where every ounce counts, and is resistant to rain and snow. The REI Magma understands that all campers are not designed equally and offer a range of sizes for both men and women.\r\n\r\nPerformance\r\nCompared to the Teton Sports Leef 0 Sleeping Bag, the Magma sleeping bag has a similar bag review. Both are mummy bags with a high draft collar. With an ability to protect you to temperatures as low as 17 degrees F, the insulated yoke will keep you warm even when it is quite cold outside. The REI has an anti-snag zipper hybrid zipper. This means that it does not zip bottom to top, like a traditional sleeping bag, but rather on a diagonal along the shoulders down to the torso. It also has variable baffle spacing so that you get the ideal warmth and comfortable batting.\r\nDesign\r\nThe magma takes into account the typical shoulder girth of men and hip-width of women, therefore, constructing sleep sacks that are both gender-specific, as well as unisex, depending on your exact needs. It has an 850 fill power of goose down, meeting RDS and Bluesign approvals, yet it still fits nicely in the included compression sack despite its fill weight. While it is not as lightweight as the Western Mountaineering Summerlite Mummy 32F Sleeping Bag, it is still much lighter than most competitors coming in at 2.6 ounces. Both sleeping bags recommend utilizing a sleeping pad for extra comfort, but they are also not essential.\r\nValue\r\nThe Winner Outfitters Mummy is comparable as far as a sleeping bag review goes, but they differ drastically at the price point. Where the REI Co Op comes in at $379.99, the Winner Outfitters Mummy is a mere $34.99. The biggest difference is that the Winner Outfitter is filled with 200G\/\u33a1 Hollow Fiber fill, which enhances non-allergenic, pro-environmental, and better insulating performance. The REI Co Op has a Downproof Pertex shell, water-resistant 850-fill-power goose down, and a 15-denier lining. The stuff sack size is within a couple of inches of each other, as are the weight (a difference a few ounces).\r\nRei Co-Op Magma 15 Wrap Up\r\nIf you insist on having a down insulated sleeping bag and want a high-quality construction, the REI Co Op Magma 15 will not disappoint if you want to make an investment in your camping gear. Yes, there are more affordable down, mummy, sleeping bags, that have a temperature limit less than the REI, but the small details, such as the shoulder to torso zipper, in the Magma 15 add up to a great value.