A Bag So Nice, You’ll Wear It Awake: Sea to Summit Ascent Sleeping Bag Review

I could tell it was getting colder in the tent — and fast. I’d kept up with the wood furnace for a few hours, but I got tired of getting up every 30 minutes to load new logs and stoke flames out of it. Besides, I was here to test my sleeping bag, and I wasn’t going to really do that if I kept it too warm.

So, I stopped getting up and the fire died. The temperature started dropping. I knew it was going to get close to zero tonight. I could hear snow falling against the nylon walls. Eventually, I could see my breath. But I was so comfortable and warm, I dozed off within minutes, wrapped in the Sea to Summit Ascent.

In the morning when I woke up, the walls were covered in frost. My water bottle had frozen. And I didn’t want to get out of my bag to face the frigid day. Luckily, I remembered I didn’t have to. I reached down and unzipped the foot box of the bag, stuck my feet out and into my Sorel boots, and got up to make coffee. That entire morning, I wore my sleeping bag around camp.

I was really starting to like this Sea to Summit Ascent.

In short: The Sea to Summit Ascent sleeping bag is one of the most versatile sleeping bags I’ve ever used. It is jammed with features like a zippable foot box, vertical and horizontal baffles, oversized zipper collars, and more. Most importantly, though, this thing puts out heat. Or, at least, its down baffle system traps heat so well, I regularly found myself opening the multiple zipper vents to dry my sweat and cool off — even when winter camping.

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Sea to Summit Ascent III (Zero-Degree) Review

The Sea to Summit Ascent version I used was the Ascent III — the brand’s zero-degree version of this bag. I mainly got it for cold weather adventuring: backcountry ski camping, ski area parking lot car camping, hut trips, etc. I figured with 750 Ultra-Dry Down fill, the Ascent would serve me well through late fall, winter, and early spring.

And boy, was I right. The Sea to Summit Ascent bag is a warm sleeping bag. In tents, when the temp was plummeting into the single digits and down to zero (plus or minus a few degrees), I only woke up from getting cold a couple of times. And every time, that was because I hadn’t zipped the bag up all the way or I’d left the foot box unzipped, for fear of overheating.

Sea to Summit also treats the Ultra-Dry Down with a nano-level water-repellent polymer. The brand claims that Ultra-Dry Down retains 60% more loft, absorbs 30% less moisture, and drys out 60% faster than bags using regular down fill.

I didn’t get my bag too wet during testing. But I can attest that when frost and condensation got on it, and even soaked into it, the down didn’t clump up or get matted. And what little moisture it did absorb seemed to dry out quickly.

Fit

Not all bags fit the same. I once had a sleeping bag with plenty of space in the shoulders, but that had such a tapered shape that it left almost no room for my feet to move around. It was usable, though somewhat claustrophobic. I’ve had other bags that are so spacious and loosely fit, they bunch up like a blanket and clump weirdly when you move around.

Not so with the Sea to Summit Ascent sleeping bag. The relaxed mummy shape gave me enough room to sleep naturally in any position. And at the same time, I wasn’t swimming in it.

Noteworthy Features

Zippers

The zipper system on this bag is one of its coolest design features. The main zipper on the left extends from the hood to the toes. Below that, at the very bottom of the bag, a foot box zipper allows you to open the bottom up. Stick your feet out and walk around, or use it and the full side zipper to open the bag up into a full-on down quilt.

A third half-zipper on the right side allows you to unzip the top half of the bag (in conjunction with the full-size zipper on the other side). That makes it easy to sit up or to ventilate your top half without exposing your bottom half. All of this makes for a very dynamic zipper and ventilation system.

The zippers are all also protected with an oversize draft tube and draft collar, which prevents warm air from escaping from them. A lot of times, oversize zipper cuffs like these can catch and make zipping or unzipping a tricky process. But so far, I haven’t experienced that with this bag.

The full-length side zipper is also compatible with other Sea to Summit Ascent sleeping bags. Meaning you and your partner can zip together, cozy up, and snuggle through the night.

Weight

This sleeping bag is sold as a backpacking sleeping bag. For winter backpacking trips, I think the Ascent III (zero-degree) would be great. The Ascent I (25-degrees) and the Ascent II (15-degrees) would be great for spring, summer, and early fall backpacking. It is a little bulky in its stuff sack and would take up a decent amount of space. But the stuff sack comes with attached cinch straps to really compress it down.

At 2 pounds, 14 ounces, the Ascent isn’t an ultralight bag by any means. But that wouldn’t stop me from taking it on the backpacking trail. It’s a very reliable bag.

And it’s great for car camping as well. There really isn’t an outdoor situation where this bag wouldn’t be a great fit.

Horizontal and Vertical Baffles

Most sleeping bags only utilize horizontal baffles. But Sea to Summit got creative with the design of the Ascent and decided to use both. The lower half of the bag utilizes horizontal baffles, and the upper half is vertical.

Sea to Summit says that helps to prevent down from shifting around with shoulder movement. Which, in turn, maximizes warmth.

I can see how that would work — though I had no real way of testing whether it did or not. For the record: I didn’t experience the down in the torso/shoulders moving around. And I did stay maximally warm.

Extras

Sea to Summit included an internal phone pocket on the Ascent. It’s a small zippered pouch on the inside of the bag, so you can keep your phone warm while you sleep so the cold doesn’t kill its battery. That’s handy.

However, my phone — an iPhone 11 Max — would not fit. (I had to use my girlfriend’s phone to take the above photo.)

The technical hood is also designed to trap body heat in the bag. A draft collar creates a barrier around your neck that prevents warm air from getting out and cold air from getting in. However, the hood was a little on the wide side. I did have some issues with it coming off my head during the night. But you can also cinch it down with a draw cord to avoid that.

Sea to Summit Ascent Sleeping Bag: The Final Word

Try as I might, I couldn’t find a lot of places where this bag fell short. The down is water-resistant, it’s incredibly warm, the zipper system is extremely dynamic and allows for multiple different avenues of ventilation, the zipper draft tubes and collars are all but impenetrable, and cleverly placed vertical and horizontal baffles keep you warm through the night.

The biggest pitfall of this bag is that it gets too warm in certain situations — and it certainly will be between the months of May and September (but remember, I got the zero-degree version). And even when it does, I can open the Ascent up multiple different ways to cool myself off.

I like this bag. I will continue using this bag. And I’m going to be bummed when I have to put it away for the warmer months. Part of me wishes I’d gotten a 15-degree version — because I’d be happy to use this thing all year round.

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