Gear Review: Therm-a-Rest Hyperion Sleeping Bag

The Therm-a-Rest Hyperion 20 is an ultralight three-season sleeping bag that weighs in at a svelte 1.25 pounds. Meeting the requirements of cold-weather performance and light weight can be a tricky balancing act, but Therm-a-Rest has managed the task through some clever design and the use of high-quality materials. 

Here’s my look at the Therm-a-Rest Hyperion 20— both its materials and design, plus my observations from some real-world testing in the Blue Ridge Mountains of Virginia.

Therm-a-Rest Hyperion 20 At-a-Glance

Weight: 1.25 pounds
Length (regular): 80 inches
MSRP: $410 (regular size)
Warmth Rating (F): 32-degree comfort; 20-degree limit; -9 risk
900-Fill Goose Nikwax Hydrophobic Down RDS

-Shell: 10D Nylon Ripstop w/DWR
-Liner: 10D Nylon Ripstop

Therm-a-Rest Hyperion 20 Features

Down loft: The Therm-a-Rest Hyperion 20 is filled with 900-fill Nikwax Hydrophobic Down that meets the Responsible Down Standard.
Zoned insulation: The down is distributed with the bulk (70%) on the top and sides for maximum warmth.
Hood: Cinches down easily from a loose hood to a tiny air hole. The drawcord and cord lock are on the right side, and the drawcord was long enough to find easily in the dark. The cord lock itself is a bit small and was a bit hard to handle when wearing gloves. 
Zipper: Located on the left side of the bag. It features two long drawcords, one inside, one outside and was relatively snag-resistant.
DWR-Coated Face Fabric: The Hyperion 20’s shell is a 10D Polyester Ripstop.

Temperature Ratings

If you’ve got a partner, you understand that everyone sleeps differently. One person can be toasty warm while the other is curled up in a ball desperately trying to conserve heat. Ergo, take sleeping bag ratings with a grain of salt. And remember, the rating in the model name is for the bag’s lower limit. The actual comfort level falls somewhere around ten to 15 degrees above that. So, in the case of the Hyperion 20, the comfort level is going to be somewhere around 30-35 degrees—good for shoulder seasons, but approach full-on winter conditions with caution, extra layers, and maybe a bag liner.

A Couple of Cool Design Features

In a clever design move, the Hyperion’s zipper only extends partway down the side, leaving a completely sealed and draft-free foot box. This eliminates zipper weight and increases warmth in one stroke, but it does mean you can’t completely unzip the bag to use as a quilt on warmer nights. And this 60-year old hiker’s knees weren’t always happy about the extra contortions this necessitated when sliding into the bag in the tight confines of my single-man tent. 


A welcome feature of the Hyperion are the SynergyLink™ Connectors. That’s a fancy name for a pair of removable straps attached to the underside of the bag. Wrap them around your sleeping pad and your bag stays where you want it, right on top of your insulation. It’s a godsend for restless sleepers like myself, who invariably find themselves sliding off their sleeping pad during the night.


I’m a side sleeper, so mummy bags and I haven’t always had a comfortable relationship. It’s not unusual for me to wake up in the middle of the night, disoriented and twisted into a fair approximation of a pretzel. The Hyperion is cut more generously around the hips than some other mummy bags I’ve used, so it gave me a bit more room to pull my knees up and sleep in comfort without getting tied into a knot. That’s a big difference maker for my sleeping comfort.

The Hyperion 20 comes in three sizes, ranging from 73 to 85 inches in length. For this compact 5′ 9″ backpacker, the 80-inch regular model was a fine fit.

In the Field

After checking out the particulars of the Hyperion in the climate-controlled comfort of my home, it was time to see how Hyperion worked in the field. In March I took a trip into the Three Ridges Wilderness to work on my off-season conditioning and give the Hyperion a go.


The Hyperion 20s 900-fill down packed down quite easily into the provided compression sack, taking up surprisingly little space. I typically use an Enlightened Equipment 850-fill 20-degree quilt, and I was surprised how favorably the Hyperion compared, both in packed weight and size.

Water Resistance and Moisture Management

Cold and damp spring conditions can really put a sleeping bag to the test, particularly when you add the condensation of a single-wall shelter into the mix. The weather for my trip provided a good test since a damp spring had left the forest and understory wet, while during the trip the weather provided overnight lows in the 30s and 40s, with a surprise overnight snow shower in the mix for good measure.

The DWR-treated shell and hydrophobic down of the Hyperion handled these conditions with ease. Dripping condensation from my shelter mostly beaded up on the surface of the bag, and although one particularly persistent drip wetted through the shell (note to self: redo tent seam sealing). Despite that, the down itself stayed dry and I didn’t even notice the water until morning.


The Hyperion proved comfortable on the trail, thanks in part to two features I’ve touched on earlier. The generous cut around the hips let me sleep on my side without too much bother, while the attached straps held me firmly on my sleeping pad even on an uneven campsite during my second night. Most importantly, I stayed quite warm without having to add extra sleeping layers.

After-Trip Thoughts

The Hyperion 20 served me well during my short expedition. It was warm in cold and damp conditions, packed small and carried light, and was comfortable for sleeping. It was extremely well suited to a typical shoulder season trip in my local mountains.

There were few negatives to be found. The lack of a full-length zipper did make entering and exiting the bag a little more difficult, particularly when compared to my regular backpacking quilt. And I did find the cord-lock for the hood to be a little small to handle easily, particularly for cold hands in the dark. These were small points that didn’t cast much of a cloud on my overall positive impressions of this sleeping bag.

Comparable 20-Degree Bags

Big Agnes Hitchens UL 20º 

Weight: 1 pound, 11 ounces
MSRP: $530
Fill: 850 fill down.

REI Igneo 17

Weight: 2 pounds, 2 ounces
MSRP: $299
Fill: 700 fill down

Western Mountaineering Alpinlite 20

Weight: 1 pound, 13 ounces
MSRP: $570
Fill: 850 fill down

Other Temperature Options From Therm-a-Rest

If you need something warmer, Therm-a-Rest offers two bags with a warmer rating. The Oberon is rated to 0 degrees, weighs in at 2.5 pounds, and retails for $479. The Polar Ranger is rated to -20 degrees, weighs 3 pounds 4 ounces, and retails for $699.

Looking to go a little lighter? There’s a Hyperion model rated at 32-degrees. It weighs 1 pound and retails for $349. 

The Therm-a-Rest Hyperion 20 Is a Solid Value

The Hyperion 20 is a great value in a three-season down bag. This bag could save you at least $100 compared to other 20-degree bags, while still coming in at a lighter weight, thanks to its fluffy 900-fill down. In my testing, the Oberon was a warm and packable bag, well suited to the variety of conditions you’ll find when backpacking in cold and wet shoulder seasons (sort of like March on the AT in GA, perhaps?). In my testing and limited use, the bag’s materials and construction have held up quite well, and I wouldn’t hesitate for a moment to grab it out of my bag bin for a weekend trip or a long expedition. 

Shop the Therm-a-Rest Hyperion 20 Here

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