The Big Agnes Sidewinder SL 20 has a big selling point above other bags, and that is its side sleeping design. The bag is filled with water repellent down, and additional synthetic insulation in key areas like the hips and footbox. It’s got a lower fill power than the other bags in this test, and is comfort rated to +1 degrees Celsius – so it’s less warm than others here. There’s a combination of horizontal baffles around the bag, but a grid pattern immediately next to the zip, which does a good job of keeping the down in place. The shell material is also water repellent, as is the lining.


Rating: 4/5 | Price: $299.95 | £245 | Available from: Alpine Trek | Weight: 1216g for regular, 26g stuff sack | Fill: 650 FP Downtek with Fireline Eco Synthetic Insulation | Shell: Nylon ripstop with water repellent finish | Zip: 2 way full length middle zip | Length: 178cm for regular | Rating: Comfort +1c | Sizes: Petite & regular | Men’s version: Yes

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The two-way zip runs full length down the front of the bag, with an anti-snag zipper, although I do find that it does get snagged on the fabric still. The zip pulls are quite small and so are harder to find from inside the bag. There are no other venting options.

The hood is a very nice size and shape, allowing your head to get fully tucked in, and has a draft collar around the outside. This can be cinched in, with the drawcords tucked inside the hood, meaning you don’t need to unzip to adjust. There’s no collar around the shoulders, but it’s snug fit anyway, so I don’t feel like it’s needed. There’s a mesh pillow barn right around the outside, which is also accessed from inside the hood, for adjusting as you turn. The zip has a draft tube on each side, with one bigger than the other so they slot together to keep out drafts. An internal pocket is just about big enough for a phone.

The bag is a classic mummy shape, although the women’s model doesn’t taper as tightly, giving more room at the hips. But with the zip up the middle, and a shaped footbox, the bag definitely moves with you, and can be used for any sleeping position without losing where the zip is!

It comes with a mesh storage bag and a stuff sack, but a major downside is the stuff sack doesn’t have compression straps. If I was looking at buying this bag, I would get a compression drybag alongside it, but given the lower price, it would still work out overall cheaper.

This Big Agnes Sidewinder SL 20 model is a lovely bag for side sleepers who are maybe not planning to be out on the coldest nights, but still deals well with temperatures that hover around freezing.