Big Agnes Sidewinder SL 20
Rating
Versatility: 6
Size/Weight: 4
Features: 6
Construction: 7
Sleep Quality: 7
OVERALL: 6.0
Our top pick for side-sleeping comfort.
The Big Agnes Sidewinder SL 20 is designed specifically for side sleepers, with extra room where it counts and thoughtful features that make moving around in your sleep feel natural. It’s warm, well-built and surprisingly packable for a bag this comfortable.
Best For: Side sleepers on spring-to-fall backpacking trips
Pros: Spacious in key areas, stays warm and cozy
Cons: Slightly bulky and not ideal for ultralight trips
Verdict: A smart, comfy choice for restless sleepers on the trail
Skip ahead to First Impressions, Sleeping Experience, Features Analysis, Construction and Durability, or the Final Verdict, or check out how the Big Agnes Sidewinder SL 20 compares to others in our list of the Top 5 Sleeping Bags.
Specs:
Packed Size: 8x17.5in
Weight: 2lbs 4oz
Fill: 650 DownTek™ and FireLine™ Eco
Approx Price: $249.95
First Impressions
If you’re someone who sleeps on their side and often feels like a burrito in a traditional mummy bag, the Big Agnes Sidewinder SL 20 will be a game changer. From the moment you crawl into it, the difference is clear. It’s shaped with side sleepers in mind, giving your knees and elbows a bit more room to move. This is not your average sleeping bag as it’s made to move with you, not twist around you. We found it to be a thoughtfully designed bag that’s clearly made for folks who toss and turn through the night. It also comes in a few different temperature ratings and lengths, so you can pick the one that fits your needs and height.
Sleeping Experience
The Sidewinder sleeping bag feels noticeably more comfortable than most traditional designs, especially if you like to roll from one side to the other. Even with its mummy shape, it doesn’t feel overly tight. The extra space around the knees and shoulders lets you curl up just like you would at home. The insulation is well-placed, keeping you warm without hot spots or cold patches and it feels soft whether you’re wearing a base layer or sleeping in just your skin. That said, the hood can feel a little odd if you end up lying on top of it, so that’s something to keep in mind. For colder nights in spring and fall, it really shines, but for warmer summer evenings, though, it might be a bit much.
Features Analysis
There’s a lot to like about the Big Agnes Sidewinder SL 20 when you dig into the details. The hood fits snugly like a jacket and even has a stretchy pocket to keep your pillow from sliding around in the night. A smart no-draft zipper and insulated collar keep the cold air out, and the bag includes small loops on the outside if you prefer to hang it for storage. It also comes with a stuff sack for packing, though you might want to swap it out for a smaller one if saving space is a priority. While it’s not packed with flashy extras, everything here serves a purpose, especially for side sleepers.
Construction and Durability
Made from nylon ripstop on the outside and lined with soft polyester taffeta, the Sidewinder SL 20 feels durable and comfortable. It’s coated with a PFAS-free water-repellent finish, and the down insulation is treated the same way to help it handle a bit of moisture. Still, like all down bags, it’s not totally immune to getting damp from condensation. One thing we noticed is that some of the down can shed, which isn’t ideal, but also not uncommon in lightweight sleeping bags. The bag holds up well in most 3-season settings, but if you’re going to be out in freezing or wet conditions for days on end, you may want something burlier.
Final Verdict
Our Big Agnes Sidewinder review boils down to this: if you’re a side sleeper who wants better sleep outdoors, this bag is worth a serious look. It isn’t the lightest option out there, so hardcore ultralighters might hesitate, but it’s well balanced due to it being warm, thoughtfully designed and packing down reasonably small. It’s not built for winter camping or extreme alpine adventures, but it’s a good sleeping bag for spring, summer and fall backpacking or car camping. At just over two pounds, it's light enough for most uses without giving up comfort.
Why not visit our list of the Top 5 Sleeping Bags of 2025 to see how The North Face Blue Kazoo compares?
Water & Outdoors reviews are written by our staff writers, who combined have over fifty years of experience on the water and outdoors. We may earn commissions if you choose to buy through a link you’ve clicked on our website, however this does not influence our reviews. For more information, please see our Editorial Policies.