Sea to Summit Ascent AcII Sleeping Bag Review

On my last thru-hike (PCT, 2021) I used a quilt for the first time. Thanks to (mostly) cooperative weather, a 20-degree quilt proved to be just enough to keep me warm throughout four months of hiking, though there were a handful of close calls.

On those nights, I woke and found myself lusting after a good ol’ full-size sleeping bag. And that’s a good description of the Sea to Summit Ascent AcII. It’s not lightweight, but it’s far from ungainly, and it’s loaded with features considering its (relatively) modest weight. It packs easily and reasonably compactly. It’s comfy and it’s warm.

This is a nice bag to have in my quiver for those nights/trips where the cold is just a little too much for my quilt.

Sea to Summit’s Ascent AcII 15-degree bag is a solid three-season option for long-distance hikers. Photo by Clay Bonnyman Evans.

Sea to Summit Ascent AcII Sleeping Bag At-a-Glance

MSRP: $419.00 (15 F)
Temperature rating: 15 degrees F
Total weight: 39 ounces | 1100 grams (not including stuff sack)
Length: 78”
Width: 61” (shoulder), 57” (hip), 48” (footbox)

Compressed volume: 6.2 liters
Fill: ULTRA-DRY™ 750 FP 90/10 premium grey duck down
Lining/shell fabric: 20D nylon

Accessories: Stuff sack, cotton storage sack

How It Was Used 

I used the bag two nights in a tent with temperatures down to 35 degrees and indoors every night throughout the winter months.

sea to summit ascent acII

Sea to Summit’s Ascent AcII offers plenty of versatility and ventilation options. Photo by Clay Bonnyman Evans.



This Sea to Summit sleeping bag is a warm, thoughtfully-designed hybrid between a true alpine “mummy” bag and a traditional rectangular bag. It’s burly enough to handle some serious cold during an early-season long-distance hike, loaded with features and reasonably light considering its temperature rating.

For those who feel claustrophobic in a mummy bag — “rotisserie” sleepers like me, for example — the Sea to Summit Ascent AcII is roomy enough to keep you rolling happily through the night. Yet somehow, it stuffs down to a surprisingly manageable volume.

  • Vertical chest baffles prevent clumping and cold spots
  • Full-sized main, side, and foot zippers
  • Zip-coupling allows for pairing with another bag
  • Three-season ventilation and versatility options, including 27-inch half-zip that flips down so bag can be used like a comforter
  • Oversized draft tubes on zipper and collar to prevent heat loss
  • Internal phone pocket
  • Comes with compression and storage bags
sea to summit ascent acII

A generous phone pocket is one feature of Sea to Summit’s Ascent AcII three-season sleeping bag. Courtesy Sea to Summit.


Ultralighters will balk, but for the warmth and number of features, the Ascent is reasonably light at just 38 ounces. It’s a full bag, not a quilt, and it kept me more than warm in near-freezing temperatures; I would absolutely trust the bag down to around 20 degrees F.


At 78 inches, this is a long piece compared to my other bags. I’m not a tall person, but I tested a regular and found it plenty roomy. Because of the generous circumference all along the bag, I never felt claustrophobic or got tangled up while doing the roll-over, roll-over thing I always do.


It’s thick, silky, and squishy — what’s not to love? Seriously, what did manufacturers figure out in the last 20 years that allows them to create such durable, yet incredibly comfy materials? Honestly, I enjoy just lying atop the Ascent while reading in bed. It’s that pleasant and enveloping.

READ NEXT – The Best Sleeping Bags for Thru-Hiking


There’s never a good way to gauge durability when first testing a product intended for long-term use. But this bag, unlike more lightweight models, is beefy indeed. The zipper are full-size and protected when closed by snap-flaps. As with any lighter material, you’re well-advised to keep it away from errant campfire sparks (my bete noire; every single bag, quilt, or coat that I’ve used backpacking has little holes in it … thank goodness for Tenacious Tape!)


This sturdy, warm bag can be crammed down into a reasonably compact 12”x8”x7” without too much effort. That’s not tiny, but it fit snugly and made a solid foundation at the base of my beloved Gossamer Gear Mariposa 60 pack.

sea to summit ascent acII

The Ascent AcII packs down to a reasonably compact package.

Sea to Summit Ascent AcII 15 Pros

Warm: I’ve never felt the need for a 15-degree bag while thru-hiking, but on several occasions, a 20-degree bag or quilt has teetered right on the verge of not enough. That extra five degrees would have made a big difference the night I foolishly cowboy-camped on the banks of the South Fork Kern River during my 2021 PCT thru-hike.

Comfortable: It just feels good, this bag. As mentioned above, it’s so smooth and silky that I like lying on it even at home, while reading or hanging out.

Sturdy: This is one bag you don’t have to worry about breaking willy-nilly. The components are full-sized and the material, while pleasant to the touch, is not gossamer-thin.

Versatile: The zippering system allows for all kinds of configurations to air out feet, chest, legs, you name it. And for those cold nights, you can zip up super snug and tight, with a cinched hood and generous baffles to fend off the prying fingers of the night.

Promotes intimacy: That’s right, folks. Well, it does if you happen to be a long-distance hiker lucky enough to have a significant other who is also crazy enough to want to sleep on the ground and walk 20+ miles a day for months at a time. I didn’t have a second bag, but I’ve seen photos and I love the way you can mate two Ascents to make a cozy couples’ nest.

sea to summit ascent acII

Couples with Sea to Summit Ascent AcII bags can mate … their bags. Courtesy Sea to Summit.

Sea to Summit Ascent AcII 15 Cons

Price: At over $400, you’re definitely making an investment in this bag.

Weight: Perhaps I’ve become spoiled. Or maybe a snob. At any rate, 38 ounces isn’t a ton of weight (especially when compared to the 14-pounders I used to haul around as a Boy Scout lo, these many years ago…). But for ounce-shavers, it may be just a tad heavy.

Volume: While the stuffed bag fit snugly in the bottom of my 60-liter pack, it might be a bit of a room-hog in a smaller pack.

Slightly confusing: Sea to Summit says that the Ascent can be unzipped “fully to use as a comforter,” but I still haven’t figured out just how that works. Perhaps I’m just a dimwit!

sea to summit ascent acII

Sea to Summit’s three-season Ascent AcII sleeping bag. Photo by Clay Bonnyman Evans.


The Sea to Summit Ascent AcII 15-degree sleeping bag is a keeper, for those willing to take on a few extra ounces for sturdiness and features that will keep you warm. It’s a true three-season bag, thanks to various clever (apparently too clever, for this reviewer) features that provide tons of ventilation options and, as mentioned, mating with your sweetie. (No, not that kind of mating; OK, maybe that kind of mating, but that’s not what I meant.) Guessing it’s a few ounces too far for weight-conscious thru-hikers, but then again, the Smoky Mountains or the Sierra Nevada in early spring can get mighty cold.

Shop the Sea to Summit Ascent AcII 15 Sleeping Bag

Comparable Products

Big Agnes Torchlight UL 20

MSRP: $399.95-$419.95
Total weight: 36 ounces
Girth: 60-70” (shoulder), 36-46” (hip)

REI Co-op Magma 15

MSRP: $379-$399
Weight: 28 ounces (1 pound, 12 ounces)
Girth: 63” (shoulder), 57” (hip)

Western Mountaineering UltraLite 20

MSRP: $510-$540
Weight: 29 ounces (1 pound, 13 ounces)
Girth: 59” (shoulder), 51” (hip)

The Sea to Summit Ascent AcII sleeping bag was donated for purpose of review.

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Comments 3

  • Russell : Apr 21st

    Super weird photos with throw away water bottles and white dress shirt.

    • Clay Bonnyman Evans : Apr 21st

      It’s posed. The author’s wife.

      Smart Water bottles are a thru-hiking go-to. That very bottle is on the CDT with the author this very minute.

      As is that REI shirt (though it’s quite a bit filthier now).



  • Richard : Jun 24th

    Great Review!


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