Review: Therm-a-Rest Hyperion 32F Sleeping Bag

Ultralight Sleeping Bag
Therm-a-Rest Hyperion 32F/0C
$490, 1 lb. 1 oz. (regular)
Sizes: small, regular, long

Why spend more money on a sleeping bag? Logical question, of course. But for any backpacker eager to shave a pound or more and significant gear volume from his or her backpack, an ultralight down bag offers one of the best ways of realizing that objective—as well as delivering maximum warmth per ounce. And one of the lightest and most compact bags in this category, Therm-a-Rest’s Hyperion 32F/0C, measured up in every way on a six-day backpacking trip in the Grand Canyon in May; a six-day float trip down Idaho’s Middle Fork of the Salmon River in July; a three-day hike on the Teton Crest Trail in August; a five-day, late-summer hike in the Wind River Range; and on chilly, rainy spring nights that pushed the bag’s limits camping in May in Idaho’s City of Rocks National Reserve.

The Hyperion’s EN comfort rating of 41° F/5° C and limit rating of 32° F/0° C fell right in line with my experience: Sleeping in a tent at the City of Rocks on a night that dipped into the high 30s, I was warm enough in underwear, socks, and a warm, long-sleeve top, but felt like the bag was at its comfort limit for me. On the Teton Crest Trail, I also had a night in the high 30s where I needed a top and bottom layer to stay warm. In the Grand Canyon in early May and on the Middle Fork in July, nights only dropped to around 50° F, a temperature for which the bag was comfortable unzipped—although I slept out under the stars most nights on the Middle Fork, and on breezy nights by the water, the air cooled enough for me to zip the bag up and feel perfectly comfortable.

I don’t get cold very easily, so someone who does might not want to push this bag’s—or any bag’s—comfort limit. But given the Hyperion’s extraordinarily low weight, it makes sense and reduces your pack weight even if you need to wear a layer of clothing that you’re carrying, anyway.

Therm-a-Rest-Hyperion-32F/0C sleeping bag.
Therm-a-Rest-Hyperion-32F/0C sleeping bag.

But with just a half-length zipper (for weight savings), you can’t truly open it up and use it as a blanket on very mild nights. Still, I found it quite functional on mild nights unzipping it as far as it opens, tucking my feet and lower legs (which generally do not overheat) inside the bag’s bottom half, and opening the upper bag to use as a blanket over part of my torso.

The bag’s design places 70 percent of the insulation on the top and sides and 30 percent on the bottom/back side—ideal for back sleepers, a bit less so for side sleepers (like me), although my back did not feel noticeably colder. The draft collar and comfortably close-fitting, adjustable hood gave me a nice, snug seal on those chilly nights at the City of Rocks, while the lightweight zipper moves as smoothly as any I’ve seen on a sleeping bag, and doesn’t snag.

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Therm-a-Rest-Hyperion-32F/0C sleeping bag.
Therm-a-Rest-Hyperion-32F/0C sleeping bag.

The Hyperion is stuffed with nine ounces (in the regular) of 900-fill down—nearly the highest-rated down you can find—which translates to more warmth and packability than most bags of the same weight (and effectively, since few bags are this light, it’s as warm as bags several ounces to a pound or more heavier). According to Therm-a-Rest, the water-resistant Nikwax Hydrophobic Down used in this bag retains its loft up to 60 times longer, absorbs 90 percent less water, and dries three times faster than standard down. Box-baffled construction uses mesh walls to maximize loft and minimize cold spots, and the ThermaCapture lining features a reflective coating that increases the bag’s thermal efficiency without adding weight or bulk.

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Therm-a-Rest-Hyperion-32F/0C sleeping bag.
Therm-a-Rest-Hyperion-32F/0C foot end.
Therm-a-Rest-Hyperion-32F/0C bag stuffed.
Therm-a-Rest-Hyperion-32F/0C bag stuffed.

The fit is generous at the hood, shoulders (57-inch girth), and through the hips (49.5-inch girth) for a person of average build, though a little snug in the legs (43-inch girth at the footbox).

The 10-denier ripstop nylon shell fabric, treated with a DWR (durable, water-resistant coating) to repel moisture, is as light as bag shells get—handle it with care to avoid tears—but my bag has seen no damage and shouldn’t with sensible use. Two removable straps on the bag’s bottom side allow integrating it with an air mattress (also most useful for back sleepers).

It comes with a compression stuff sack and packs down to roughly twice the size of a liter bottle—much smaller than most similarly rated bags.

There’s also a Hyperion 20F/-6C version ($410, 1 lb. 6 oz.).


Warmth for its Weight
Warmth When Wet

The Verdict

Among the lightest and most compact down bags, the Therm-a-Rest Hyperion 32F/0C packs a huge warmth-per-ounce ratio and is a good value for ultralighters, thru-hikers, or any backpacker who wants to sleep comfortably at night and carry less weight on the trail.



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See all of my reviews of sleeping bags that I like and all of my reviews of backpacking gear, and my articles “Pro Tips for Buying Sleeping Bags” and “10 Pro Tips: Staying Warm in a Sleeping Bag.”

Want to make your pack lighter and all of your backpacking trips more enjoyable? See my story A Practical Guide to Lightweight and Ultralight Backpacking.” If you don’t have a paid subscription to The Big Outside, you can read part of that story for free, or click here to download that full story without having a paid membership.

NOTE: I tested gear for Backpacker Magazine for 20 years. At The Big Outside, I review only what I consider the best outdoor gear and apparel. See my Gear Reviews page at The Big Outside for categorized menus of all of my reviews and my expert buying tips.

—Michael Lanza


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