Big Agnes Anthracite 20° sleeping bag review: cozy, comfortable and warm in temperatures down to zero

Big Agnes Anthracite 20° sleeping bag: first impressions

The Big Agnes Anthracite 20° sleeping bag is a very comfortable, lofty and warm three-season sleeping bag from Colorado-born Big Agnes. Manufactured from a fully recycled shell and filled with FireLine Pro Eco recycled synthetic insulation, the bag is designed to be a reliable and environmentally friendly sack to fall asleep in after long days out on the trail.

In classic mummy style, this bag features a large hood that can be cinched down tight in cold conditions, a wide shoulder baffle to trap in heat and a large zip along the length of the bag that comes with a huge loop suitable for opening and closing when you’re wearing a pair of chunky hiking gloves.

The Big Agnes Anthracite 20° is designed to keep you warm in temperatures hovering around freezing. With a lower limit of -6°C / 22°F and an extreme rating of -23°C / -9°F, you can be confident that this bag will perform well in three-season conditions, though you may want to invest in something considerably warmer for the coldest winter nights.

When it comes to the bag’s weight, however, the Anthracite 20° comes in at a rather heavy 1.24kg. While this means the bag is absolutely not lightweight, it’s clearly comparable to other models out there that deliver similar temperature ratings, such as The North Face Cat’s Meow.

And the same applies to its compressibility: the Anthracite 20° comes with a tube-like compression sack that does a reasonable job at reducing its size, though we found that you can compress it down much smaller if you resort to using a dry bag as a vacuum pack and properly squeeze all the air out of the bag.

Big Agnes Anthracite 20° sleeping bag: in the field

To test the Big Agnes Anthracite 20°, I used it on several occasions through the end of summer 2023 and into fall. I used it on a rainy night in Bannau Brycheiniog National Park and a couple of times out on Dartmoor where I hiked around 15km before getting set up. Each time, the temperature dropped down into single digit conditions, with the night in the Brecon Beacons topping out at around 7°C. I never once felt cold in the Anthracite 20°, which shouldn’t be any major surprise considering it didn’t come close to the extremes this bag is supposed to be able to handle. 

Which, unfortunately, remains a bone of contention for me, forcing me to raise an eyebrow every time I look at the bag, especially considering the decision to attach a large label with Anthracite 20°F / -7°C written in bold across the front of it. As is the case with most sleeping bag manufacturers, Big Agnes seem to have opted for marketing over function here, as there’s simply no way I’d take this bag down to such extreme temperatures. Even their own internal benchmarks have the bag’s lower limit listed as -6℃, for example. That being said, I’d be confident in taking this thing down to freezing as long as I used it with a suitable sleeping pad – and I’m a remarkably cold sleeper.

In regards to the design of the bag, Big Agnes have included some clever features to ensure you keep warm in the places you need to keep warm most. The back of the bag comes with noticeably less insulation, for example, while the top of the bag feels about twice as thick. What’s more, the zipper is almost the full length of the bag, stopping only about 25cm above the foot box. This means you can open the bag almost into a blanket of sorts, adding an extra layer of versatility to the Anthracite 20° and helping you to keep a little cooler when camping at warmer temperatures. 

Another thing I appreciated is the oversized toggle on the zipper itself: despite being too small for thick mountaineering gloves, I found I could easily open and close the zipper while wearing a pair of thinner gloves.

When it comes to the bag’s length, I’m 5ft 10in (177cm) and found the regular size to be plenty long enough for me. The baffles captured my shoulders really well, and I could comfortably cinch everything down to trap in as much heat as possible.

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