GEAR REVIEW: Therm-a-Rest Hyperion 20 Sleeping Bag

By Will Rietveld

In spring 2019, Therm-a-Rest, a division of Cascade Designs, introduced some seriously lightweight and technically advanced gear. The Hyperion 20 sleeping bag (and its companion Hyperion 32) is in that suite.

I tested the Hyperion 20 for summer backpacking. I previously used and recommended a 30F bag for summer backpacking, but as I get older I get colder and prefer a 20F rated bag. I also prefer a bag with enough shoulder girth to wear at least an ultralight insulated jacket inside to increase bag warmth when needed. So how did the Hyperion 20 meet those needs?

The Therm-a-Rest Hyperion 20 sleeping bag, new for spring 2019, features 900 fill-power Nikwax water-resistant down for warmth, a half-length zipper, and lightweight materials throughout to achieve a weight of just 20 ounces for size Regular.

Specifications and Features

Manufacturer	Cascade Designs (www.cascadedesigns.com)
Model	Therm-a-Rest Hyperion 20 Sleeping Bag
Temperature Rating	20F (EN tested to 32F Comfort, 20F Transition, -9F Risk Range
Sizes Available	Small, Regular, Long (size Regular Tested)
Bag Girth	Shoulder 57 in, hip 49.5 in, foot 43 in (size Regular)
Shell Fabric	10D nylon ripstop (shell and lining, DWR on shell)
Insulation	13 oz of 900 fill-power down (size Regular)
Weight	20 oz, measured weight 20.5 ounces
Features	Box baffled construction, zoned insulation, single pull half-length zipper with inside and outside pull loops and a tab and snap at the top, zipper baffle and hood rim baffle, 2 removable stretch pad straps on the bottomside, stuff sack and cloth storage bag included
MSRP	Small $390, Regular $410, Long $430

Description

When I first saw the Hyperion 20 at the summer 2018 Outdoor Retailer trade show, it featured TARs ThermaCapture technology, which is a thin heat-reflective film inside similar to that used in their NeoAir sleeping pads. However, it was later dropped due to “manufacturing and environmental reasons”. I was hoping to test that technology, it could have made a significant difference, but there were certain concerns about toxic fumes inside the bag. However, 13 ounces of 900 fill-power hydrophobic down is about right for a 20F rated sleeping bag without ThermaCapture.

The bag' s box baffled construction is basically thin mesh (think mosquito netting) baffles shaping and separating the down chambers. And the zoned insulation means that 70% of the down is on the top and sides and 30% is on the bottom. Down on the bottomside gets compressed, and presumably a sleeping pad provides supplemental insulation.

I note that the temperature rating implied for this bag is 20F, which suggests it’s comfortable at 20F. That’s not quite true; the EN test says that its comfortable at 32F, the end of comfort arrives at 20F, and at -9F your life is in danger.

Sleeping bag warmth ratings and sleeper warmth is complex, and a disclaimer is often provided. The equation consists of factors like the amount and fill-power of the down, bag girth (a slimmer bag is warmer), and bag construction. A bag’s warmth rating is just one factor to evaluate it; other useful factors are the bag’s fill weight (13 ounces for Size Regular), double layer loft (4.5 inches in this case), and shoulder girth (the specification for the Hyperion in size Regular is 57 inches, but we measured it at 58.5 inches). And, of course, people vary in how well they stay warm.

For me, the red flag on this bag is its specified 57-inch shoulder girth. That data was not available when I received the bag, but I assumed it was similar to other TAR bags, like the Parsec 20 which is 62 inches. Ultralight backpackers like me will love the bag’s 20 ounce weight, but the tight shoulder girth may limit wearing any insulating clothing inside (see field testing section).

The Hyperion’s 10-denier shell and lining fabric is a good weight saver; it’s hard to go much lighter than that. Also its half-length single-pull zipper (it looks like a #3) saves a little weight. Single-pull means it’s sewn in at the bottom, has only one slider, and won’t separate.

Overall, TAR has done a diligent job of trimming weight and maximizing warmth of the Hyperion 20.

Field Testing

I tested the Therm-a-Rest Hyperion 20 on seven trips: one spring car camping trip in the Southern Utah backcountry and six backpacking trips in the Southern Colorado Rockies. The lowest temperature encountered was 34F. I slept under the stars, in 3-person double-wall tent, in a 1-person floorless Dyneema shelter (shown), and in a 1-person silnylon single-wall tent.

In spite of the bag’s slender shoulder girth, I initially tried sleeping in the bag wearing a full complement of UL camp clothing (thin baselayer + ultralight synthetic insulated jacket + ultralight down jacket.) The jackets were not as bulky as they might sound, weighing 6 ounces and 5.9 ounces, respectively. With those clothing items worn, I found it very difficult to completely zip up the bag, and it was necessary to snap the tab at the top of the zipper to keep it from opening on its own. I’m 6 feet tall and the bag (rated to 6 feet) just barely fit my length.

Next I tested the bag wearing only a thin baselayer and the ultralight down jacket described above, and that made a remarkable difference – the bag felt much roomier inside and the zipper was fairly easy to fully close and secure with the tap and snap. I wore that clothing combination (thin merino baselayer plus Montbell Plasma 1000 down jacket) inside the bag on my next five backpacking trips.

Note that the zipper curves at the top to the base of the hood. When the bag is tighter, as with wearing too much clothing inside, the zipper is hard to operate and snags more because of the tension on the zipper. I got along with the small zipper and its two cordloop pulls a lot better when I wore minimal insulated clothing inside.

As far as bag warmth, I stayed warm in the Hyperion 20 down to 34F one night, and numerous nights in the 40sF, but I was not able to test the bag’s 20F lower limit during my testing. The bag’s fill weight of 13 ounces of 900 fill-power down is about right for a 20F bag rating, so the Hyperion 20 is on target with comparable bags. A simple method to compare bags with different down fill-power is to multiply the fill weight by the fill-power to get the total down volume in cubic inches.

I found the bag’s removable pad straps on its bottomside handy for helping to hold a sleeping pad in place, especially a slippery one like the Therm-a-RestNeoAir Uberlite I co-tested with the Hyperion. If they are not needed they are easily removed to save a smidgeon of weight. Note that using the pad straps conflicts with side sleeping.

The bag’s hood adjustment is a one cord design with an external cord loop and anchored cordlock. Pull on one side of the loop to snug one side of the hood; pull on the other side of the cord loop to snug the other side of the hood.

Assessment

Overall I found the Therm-a-Rest Hyperion 20 quite liveable and warm, despite its slender shoulder girth. Fortunately the measured shoulder girth (58.5 inches) was a little roomier than the specified shoulder girth (57 inches), and that relatively small amount made a big difference. The Hyperion works for me if I limit clothing inside to a thin baselayer plus a thin ultralight jacket. That allows me to get the zipper closed without much snagging and the top tab snapped to keep it zipped. Legwear is a lesser issue regarding room inside the bag. This basically makes the Hyperion 20 a summer bag for mountain backpacking; it likely will be chilly in the shoulder seasons.

Readers might be wondering what the circumference of my upper body is so they can evaluate their fit in this bag; I’m 44 inches around my upper arms wearing a thin baselayer, and 47.5 inches wearing the baselayer plus a thin down jacket. My advice is to measure your shoulder circumference wearing similar clothing before you consider the Hyperion. If you are at or below my dimensions, you are good; if you are larger or prefer to wear more clothing inside your sleeping bag, look for a roomier bag. Or consider getting the Hyperion size Long to get an extra inch of shoulder girth.

The MSRP of $410 for the Hyperion 20 Regular length is a good value for a 900 fill-power down insulated ultralight sleeping bag. And its 20-ounce weight is hard to beat – 13 ounces of down and 7 ounces of other materials – it’s the same weight as many ultralight 30F down sleeping bags.

Overall, Therm-a-Rest is solidly into the ultralight down sleeping bag market with the Hyperion 20 being a good choice at 20 ounces for a 20F down bag. Interestingly, Therm-a-Rest has a Better Sleep Guarantee, which they describe as “All Therm-a-Rest sleeping bags and quilts are covered by our Better Sleep Guarantee. When you wake up on a Therm-a-Rest sleeping bag or quilt, we're confident you'll wake up feeling better than ever. If you are not completely satisfied, return it within three months with the original receipt of purchase and we will give you a full refund- no questions asked.” They stand behind their bags!