Big Agnes Bellyache Mountain SL Sleeping Bag

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With this new technology, you may actually want to backpack in the rain. Big Agnes Bellyache Mountain SL mummy sleeping bag features DownTek™ water-repellent down insulation.

  • Features

    • DownTek 700-fill-power duck down repels water employing nano technology and a proprietary process to apply a micro-thin polymer to the down
    • DownTek down repels water and maintains loft and insulation value, even when exposed to moisture
    • Proprietary application process creates a water repellent, antimicrobial and antibacterial down insulation that actually floats on water
    • Vertical chambers with internal mesh gates keep insulation from shifting up and down
    • Traditional style mummy bag is designed without the integrated pad sleeve (normally found on Big Agnes System bags) and features full insulation underneath
    • European Norm (EN) is an independent third-party temperature rating, allowing accurate comparisons across brands with other EN-rated bags
    • Ripstop nylon shell has a water-repellent finish to shed water
    • Nylon taffeta lining is soft and breathable
    • Down-filled collar at top seals around the neck to prevent warm air from escaping and cold air from entering
    • Large draft tube located behind the zipper prevents warm air from escaping and cold air from entering
    • Interior fabric loops stabilize a sleeping bag liner, sold separately
    • 2-way, full-length YKK zipper zips to other bags of opposite configuration
    • Big Agnes Bellyache Mountain SL mummy sleeping bag includes a mesh storage sack and a nylon stuff sack


    Many sleeping bags are rated for temperature by an independent testing protocol. REI and the broader industry now use the International Organization for Standardization (ISO) 23537 protocol, which improves on the older European Norm (EN) 13537 standard; you may still see older items in our assortment that were only EN tested. With either protocol, each bag gets a Comfort (or T-Comfort) rating and Lower Limit (or T-Limit) rating. The Comfort rating is the lowest temperature at which the bag will keep the average "cold sleeper" comfortable, and the Lower Limit rating is the lowest temperature at which the bag will keep the average "warm sleeper" comfortable. Ratings are based on a person wearing one long underwear layer and a pair of socks, sleeping on an insulated surface with a minimum R-value of 5.38. Many brands use the Comfort rating for women's bags and the Lower Limit rating for men's and unisex bags. Everyone's body and sleep comfort differ, and conditions of use (posture, clothing, sleeping pad R-value, wind, humidity, etc.) affect total insulation, so EN and ISO ratings are intended as a guideline to help you compare products, rather than a guarantee of warmth.
    View all Big Agnes Men's Sleeping Bags
  • Technical Specs

    Best Use


    Tested Lower Limit

    17 degrees (F) - EN

    Tested Comfort


    Temperature Rating (F)

    17 degrees (F)

    Temperature Rating (C)

    -8 degrees (C)


    Ripstop nylon

    Insulation Type


    Water-Resistant Down



    700-fill duck down



    Sleeping Bag Shape




  • Reviews
    6 reviews with an average rating of 4.5 out of 5 stars

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