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Twelve years ago Big Agnes dove headfirst into the fray of designing gear for the outdoor world. It introduced the unique Big Agnes System (sleeping bags with a pad sleeve on the bottom instead of insulation) and defined a new level of comfort for hitting the sack at night. Now, for the first time since the brand was born, Big Agnes  has revived the traditional mummy bag design and redesigned its insulation and technology from top to bottom. The result is Bellyache Mountain SL17-Degree Sleeping Bag, a technical, three-season sleeping bag that conquers wet nights in the spring and cold mornings in the fall.

Perhaps the most notable feature of the Bellyache is the Downtek Insulation. This water-repellent down retains loft, breathability, and insulation value even if the down itself gets wet from rain or moisture. This gives you a serious advantage over traditional down insulation that clumps and lies flat at the first sign of moisture. Even with high-end insulation, a sleeping bag is only as good as the baffles that hold its insulation and the Bellyache uses Flow Construction, one of the most innovative baffle constructions in the industry. Insotect Flow uses a series of vertical baffles with internal gates that eliminate vertical and lateral clumping by constantly evening the distribution of insulation from head-to-toe, thus eliminating cold spots. Along with draft-stopping features like a seal around the neck opening, a wedge between the sleeping bag and sleeping pad connection, and a no-draft tube along the zipper, this sleeping bag offers reliable, regular warmth throughout the night.

Amazingly, for all its cold-and-wet-weather advantages, this sleeping bag maintains a weight well under three pounds. Along with your insulating layer and a wool hat, this versatile 17-degree bag should be an essential part of your kit whether you're pitching a tarp in the Pacific Northwest or pitching a single-wall in the Carolinas.

  • Cozy 17F-degree temperature rating keeps you toasty-warm early spring through late fall
  • Light and lofty 700-fill DownTek water-repellent down insulation won't clump up or freeze, because it won't get wet
  • Traditional mummy shape gives body-contouring, efficient warmth with some wiggle room
  • Durable nylon fabric shell resists water, and smooth nylon taffeta lining resists stains
  • Draft collar, draft wedge, and draft zipper ensure warm air stays in and cold air keeps out
  • Left- and right-zip bags mate together for a cozy coupling
  • Insotect Flow construction evenly distributes heat with flow-optimization and baffle design
  • Mesh storage sack and nylon stuff sack included for convenient storing and packing
  • Reviews
  • Q & A

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Great simple bag

  • Familiarity: I've put it through the wringer

I used this section hiking PCT washington and on countless other backpacking trips, so far I have no complaints. No leaking feathers or anything annoying. The fabric is soft and light but feels strong enough. It is a simple, warm mummy bag, what more could you ask for? I have used it down to about 27 and been just fine, the whole bag is so much fluffier than a 32 or 40 degree bag but that comes at the cost of weight, also, the zipper is a little heavier duty than I would prefer, I think they could save an ounce or two there. Overall great bag for the price I paid and I would probably buy it for the full retail price if I had to!

Update: I used this under just an ultralight tarp when it was about 21F, wearing two thin layers on the top and bottom. I was moderately warm until about 2:00am when I bang to get chilled. I put on a down coat and all but my mouth in the bag. I stayed warm enough to sleep the rest of the night but the morning sun was a very welcome sight!

Nearly perfect

  • Familiarity: I've used it several times

Great zipper setup, great loft for the price and weight, super warm down into the teens, roomy cut, and the down is incredibly water resistant. Everything you want in a bag, except one minor detail. No pad sleeve or even simple straps. I don't know why BA doesn't put some kind of pad retention method on every bag because it really makes a huge difference. But its fairly minor and easy enough to put a couple simple straps in place yourself. So all things considered I definitely recommend this bag.

Great bag for the price!

  • Familiarity: I've used it once or twice and have initial impressions

I've yet to use this in the cold. This is even my first down bag. I have to say though that it is amazing. After years of using synthetics, I will never look back. The down is so lofty and when you get in, it traps in so much warmth. I went with this bag because there aren't too many in this price range with this fill power and vertical baffles. The 700 fill may not be ultralight, but it does the job. The bag packs to about the size of a thermarest trail scout, but would be smaller with a compression sack. There is extra down around the foot and head areas. The bag overall is about 3-3.5 in. thick. And while I haven't used this in winter conditions, I slept in it one night in my house and I had to get out of it. It gets super warm. The fabric inside is super soft and is the same fabric on the bottom. The shell fabric on top is a light ripstop. I would say both fabrics are 20-30 denier. The zipper is about the best anti-snag zipper. Very nice YKK 2-way zip. The green color is a nice contrast as well. The neck baffle works well, even though it doesn't completely surround your neck. It can tuck in and block drafts and it makes it feel like a blanket. The vertical baffles keep the down in place and really move with you. I tossed and turned in it as a test and as a person that doesn't sleep still, I say its excellent for a mummy bag. I have no worries taking this to the mid 20's I'm excited for winter to come so I can test this bag. I'll update my review when I do.

downtek down in action!

check this short vid out that demonstrates DownTek's water repellent properties. You will want this bag after watching...

I think it's too good to be true. In the middle of shaking the jars, the camera cuts to black for a second. It would've been so easy to switch out the jars. And yes, I know he shook it after the camera came back into focus, but he didn't shake it for more than a second. I just hate how people can't even trust their product enough to make a solid instructional video. Even if there was some down floating in the DownTek jar, even if their was a little clumping, it still would've been better than deceiving us by cutting the camera away.

Hey Matthew, good point you make for sure. Camera on tripod would have been a good way to go with this.

I would say if you are thinking about getting a bag (or jacket, or other down piece) using the DownTek, to give it a go and it out. We have a great return policy and if the product does fail, can help you file a warranty with the company. Big Agnes does have a Life Time Manufacturer Warranty.

Buffalo River Camp Orr

    We drove in at dusk set up our tent. My son and I both have self inflating ground pads and 20 degree or better sleeping bags. I have the Big Agnes Bellyache. The first night was perfect, around 50 degrees or so, and the next two nights were about 75 degrees it seemed. The Big Agnes allowed me to sleep comfortably in my bag. I used my night clothing to regulate my temperature so I didn't over heat. The bag stayed dry even in the humid conditions we were in. I was well pleased.

    What size does this bag compress down to, I've seen 8x8.5". I want to be sure this is true as I am pressed for pack volume.

    Take a look at this review on this bag.

    It looks like it doesn't have a very good rating for packed size, i would look at the Sea to Summit Spark SP II bag.

    Also, I own a kelty ignite dridown 0 bag, and it packs super well in a Granite Gear Medium compression sack. I have to remove the divider in my backpack so that there isn't wasted space in the sleeping bag compartment. Also it is very very warm, I've camped in it on nights when it has been -10 and stayed comfortable with a tshirt and long underwear. But i have also used it when it's 40 out and been perfectly fine by just venting it at the feet. Also, it is filled with DriDown, which means it is treated, and still keeps it's loft when wet. I have slept outside in this bag with no bivy or ground cloth, and when i woke up the bag was wet, but the down was still lofty, and it was still just as warm as it was when i fell asleep. I love my Kelty and would HIGHLY recommend it.

    Does it come with a compression sack? Or its just a storage sack or stuff sack.