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Big Agnes Thunderhead SL 30 Degree Sleeping Bag

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Big Agnes Thunderhead SL 30 Degree Sleeping Bag

By Steven

Enwild Gear Specialist

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Catering to ounce-counting backpackers and thru-hikers, the Big Agnes Thunderhead SL 30 Degree down sleeping bag utilizes an innovative zipperless design and the Big Agnes Sleep System to weigh less than 2 pounds!


Catering to ounce-counting backpackers and thru-hikers, the Big Agnes Thunderhead SL 30 Degree down sleeping bag utilizes an innovative zipperless design and the Big Agnes Sleep System to weigh less than 2 pounds!

The bag is insulated with 650-fill DownTek insulation. Down insulation has long been renowned for its compressible properties and efficiency in delivering an excellent warmth-to-weight ratio. The shortcoming of down has been its susceptibility to the effects of moisture, losing much of its performance qualities when wet or damp. DownTek insulation utilizes nano technology and a proprietary application process to provide water-repellency and both anti-microbial and anti-bacterial protection. A nylon rip-stop shell further protects the insulation from moisture while providing lightweight durability.

In a traditional sleeping system, the bag lies on top of a sleeping pad. In this configuration, many people find themselves rolling off the pad at night. Plus, the insulation on the bottom of the bag is compressed by the sleeper's weight. Once compressed, the fill loses most of its insulating properties. The Big Agnes System is different, joining the bag and pad together. The pad (sold separately) slides into a sleeve on the bottom side of the bag, supplying insulation to the bottom of the bag while the top 2/3 of the bag is insulated like a traditional sleeping bag. This design provides a secure foundation so you can roll, twist and turn freely during the night without ever rolling off your pad. NOTE: Using the Thunderhead SL 30 Degree without a sleeping pad will not allow it to live up to its 30 degree temperature rating.

Vertically-structured side walls and diagonal baffles help to eliminate cold spots while keeping weight to a minimum. A unique “cocoon-style” design uses a clip-and-loop system at the top of the bag to provide entry without the need for a zipper. Combined with a tapered mummy cut, this feature also maximizes thermal efficiency. Other features include an insulated and contoured hood, a vaulted foot box, an anti-draft collar, and internal liner loops. p>

Available in Regular (fits to 6’ 0") and Long (6’ 6") lengths, each Big Agnes Boot Thunderhead SL 30 Degree sleeping bag includes a mesh storage sack and a nylon stuff sack.

  • Cocoon style construction features easy to use clip and loop system eliminating the need for a zipper
  • Oversized interior anti draft collar wraps around the entire body providing a 3D barrier against cold spots
  • Vertically structured side walls integrating diagonal baffles trap heat closer to the body
  • Vaulted foot box creates more wiggle room for your feet
  • Integrated half pad sleeve with unique design keeps you securely attached to the pad from the hips up while allowing freedom of movement for your legs, more like a traditional mummy bag
  • Superlight shell fabric with high tear strength
  • DownTek water repellent down repels water while maintaining insulating value
  • Low profile cordlock lets you un-cinch the hood with one hand
  • Interior fabric loops for sleeping bag liners
  • Exterior loops for hang drying or storage
  • Mesh storage sack & nylon stuff sack

Technical Specs

Best Use
Fill Material
650-fill DownTek
Fits To Girth
Regular: 62"
Long: 64"
Fits To Length
Regular: 6' 0"
Long: 6' 6"
Temperature Rating
30 Degrees F
Insulation Type
Item Weight
Regular: 1 lb, 12 oz
Long: 1 lb, 15 oz
Storage Sack and Stuff Sack Included
Limited Lifetime
Packed Size
Regular: 7.5" x 15" (5.5" x 6" compressed)
Long: 7.5" x 15" (5.5" x 8" compressed)
Shell Material
Nylon Ripstop w/ DWr
Liner Material
Nylon Taffeta

7 Reviews

4.43 / 5

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Light and comfortable


This is a very comfortable bag with water resistant treated down, solidly built and a unique entrance with no zipper. It really is not difficult to get in and out of, certainly not worse than a zipper, and no zipper snags to deal with in the middle of the night. I also like the "flap" at the opening because it feels like a comforter at home. The unique side walls makes a great pocket for your arms to keep them warm and not dangling off of the sleeping pad. Roomy in the knees though the footbox is fairly narrow. The down is reasonably fluffy and not clumpy - though the tag cites 80% down minimum, which I assume means some feather could be mixed in. Looking through the bag into light, I'd say feathers or dense clumps are 5% at most. As a dust-mite allergy sufferer, I've been pleased with modern treated down as the mites don't seem to colonize the material as they do for untreated down and feathers.


Only a few minor complaints: (1) the dark color is very emo, and isn't going to brighten up the tent or give a cheery feeling out in the woods alone. Very odd. (2) the opening flap has hooks to keep it in place; they are much more challenging to engage than they should be, and would be a pain getting in and out in the night. So far, I've not been using them and just tucking-in the flap. (2) the pad sleeve only supports using std. narrow pads, so your favorite wide pad isn't going to work... but you can just skip the sleeve if you are certain to not slip off the pad. There is no insulation underneath the torso - like the Sierra Designs backcountry bed or a quilt (3) the strap to secure the pad is cumbersome and difficult to connect the single spiked clip - would be be Much simpler, faster, and easier to use with a std. two-part clip. I'd like to replace it if I can find a small clip. (4) the down shifts a lot within the each tube (but not between tubes thankfully) so you need to redistribute before climbing in or even after - which is std. procedure for many down bags. (5) I doubt this is a 20 degree bag and 50 degrees may be the lower limit for cold sleepers like me. The warmth of the pad will really dictate how warm you want the bag to be. That said, it is probably too warm for summer use, but great for summer alpine trips, and it is so light and small, it would be very handy to throw on top if the night turned cold.

Chris S.


May be too specific for some


This bag has a clever design and makes a great sleeping solution when matched with the right sleeping pad. In fact you can vary the temp rating (to some degree) of this bag to your personal preference by changing between insulated and non-insulated pads. The design is simple and leaves off the frustration of a zipper, which I also love.


The problem for me relates to the range of conditions this bag would fit. A 30 degree bag makes sense for summer only if you can fully unzip and lay it on top of yourself, expose your feet, etc. That doesn't work with this bag. I will probably need a hybrid quilt to match the weight and simplicity. Again, might just be a special case for some. Otherwise, this is a great piece of gear.

Qian J.







Fermin A.


Be aware


The color


The bag requires a sleeping pad for it to actually achieve 30 degrees of warmth. I wished they had shared this before purchasing the bag. The zipperless design actually might be difficult to clip on when in the dark but I haven't tested that so that's just an assumption.

Steven P.


nice and light


packs small pad slides in and doesn't move all night



Suzanne L.


very comfortable


it is better than any i ever had


i don't have any dislikes

Andy M.


Excellent bag!


The thing I like about this bag is that, well, my fiance loved it! I haven't personally used the bag, but she had zero complaints. Thus making it the excellent bag. :)