Thermarest Hyperion Sleeping Bag Review

Justin Crossley

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When Brad Brooks from Argali Outdoors said he had a Thermarest sleeping bag to test out, I was intrigued. I didn't even know they made sleeping bags. The bag I'll be testing out is the Hyperion 20F. Retail price is $419.95 and it features 900 fill Nikwax Hydrophobic Down. I'll post an ongoing review here in this thread so subscribe at the top if you want to be notified as this goes along.

98735
 

BRTreedogs

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Interesting it's super light. I'm interested to see how big it is and how roomy for the temp rating at that weight.
 

doverpack12

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Justin it seems too good to be true for the weight vs temp rating but I'm following to find out. Interested in size as well because they don't list anything for dimensions on the website.
 

realunlucky

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That's a pretty good price point for those specs. Subscribed

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Trial153

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That’s crazy light weight for its rating. 20 Oz for a 20 degree mummy bag....what am I missing ? What was given up to get that kind of weight?
 

wind gypsy

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Justin it seems too good to be true for the weight vs temp rating but I'm following to find out. Interested in size as well because they don't list anything for dimensions on the website.
Thermarest is generous with the level of detail they provide in their specs. If you understand what the specs mean you can get a pretty good feel for how they get to these weights/ratings.

Based off the specs, here's how they get to a 20 degree bag with such low weight:
- low volume fit - compare the shoulder/hip/footbox ratings to others, they are pretty tight
- Light, thin shell fabric - 10d, WM ExtremeLite shells are 12d for reference
- High fill power down
- Zoned insulation, 70% on top, 30% on bottom. Think quilt logic minimizing underutilized insulation beneath you but still get the draft free benefits of a bag, smart.
- No neck baffle - these are common once you get to 20 or 30 degree bags and below and help seal heat in but might not be required if you have a tight seal in the hood around your head. It's nice to have them but they add a bit of weight
- Short zipper
- 20 Degrees is a EN Lower Limit, comfort rating is 32 Degrees.

So compared to a WM UltraLite with similar dimensions and a 20 degree rating, you have:
-Assume less real world warmth based on EN ratings
-Shorter zipper, have to "crawl into" the bag a bit more
-no neck baffle
-Less down insulation - I'd wager WM spec'd 850+ would test as high or higher actual loft than 900 fill in thermarest. You can shift the down in the ultralite from bottom to top, effectively "overstuffing" the baffles on top of you in the case of loft degradation.
-Treated vs untreated down
-Lower price (made in China), 9 ounces lower weight.

Functionally the 20 degree hyperion is probably closer to a WM SummerLite bag which weigh 19 ounce and have a 32 degree rating than the UltraLIte but likely somewhere between the two in warmth.
 
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Justin Crossley

Justin Crossley

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We are late in the season for cold temperatures so it will be a while before I can test the lower limits of this bag. I did use it the other night though with temps getting into the mid-thirties and was very warm. I had to leave it unzipped most the night.

100802

I am a very warm sleeper so I sweat very easily in a mummy bag. I felt the bag breathed pretty well and the material on the inside has a really nice feel to it. It has a "soft" feel instead of a kind of "plastic" feel I have noticed with a lot of bags.
 
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Justin Crossley

Justin Crossley

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I knew I would wake up to a lot of dew on everything so I intentionally didn't use a tarp or tent.

100804
 

MuleyFever

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I think in the weight race many companies cut dimensions to save weight. It's important to remember that insulation insulates with loft. If you are squeezing into a bag and compressing the insulation you are reducing its rating.
 
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Justin Crossley

Justin Crossley

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I think in the weight race many companies cut dimensions to save weight. It's important to remember that insulation insulates with loft. If you are squeezing into a bag and compressing the insulation you are reducing its rating.
I have experienced that before when my bag is too short and my feet are pressed into the bottom of the bag. The Hyperion is on the slim side but not more so than other ultralight mummy bags i've used.
 

wind gypsy

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Seems like a well thought out bag. I think it'd catch another group of buyers if they offered a version with a little more girth.
 

JakeMahonsGuideService

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Thermarest is generous with the level of detail they provide in their specs. If you understand what the specs mean you can get a pretty good feel for how they get to these weights/ratings.

Based off the specs, here's how they get to a 20 degree bag with such low weight:
- low volume fit - compare the shoulder/hip/footbox ratings to others, they are pretty tight
- Light, thin shell fabric - 10d, WM ExtremeLite shells are 12d for reference
- High fill power down
- Zoned insulation, 70% on top, 30% on bottom. Think quilt logic minimizing underutilized insulation beneath you but still get the draft free benefits of a bag, smart.
- No neck baffle - these are common once you get to 20 or 30 degree bags and below and help seal heat in but might not be required if you have a tight seal in the hood around your head. It's nice to have them but they add a bit of weight
- Short zipper
- 20 Degrees is a EN Lower Limit, comfort rating is 32 Degrees.

So compared to a WM UltraLite with similar dimensions and a 20 degree rating, you have:
-Assume less real world warmth based on EN ratings
-Shorter zipper, have to "crawl into" the bag a bit more
-no neck baffle
-Less down insulation - I'd wager WM spec'd 850+ would test as high or higher actual loft than 900 fill in thermarest. You can shift the down in the ultralite from bottom to top, effectively "overstuffing" the baffles on top of you in the case of loft degradation.
-Treated vs untreated down
-Lower price (made in China), 9 ounces lower weight.

Functionally the 20 degree hyperion is probably closer to a WM SummerLite bag which weigh 19 ounce and have a 32 degree rating than the UltraLIte but likely somewhere between the two in warmth.
Damn, that's an impressive bag! I use a Kuiu 15 degree bag and have been very happy with it. Curious how the Thermarest bag holds up
 

Tango1

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Just came out of the Idaho backcountry after a week with the Hyperion 20 degree bag. We experienced everything from 75 degrees during the day to high winds and approx 30 degrees at night. Snow at 7500’ when I hiked out this morning. I’m 5’ 7”, 135, 50 yrs old, distance runner fit, and classify myself as sleeping cold. I used the bag with a NeoAir Xlite pad inside of an old (but great) Bibler mountaineering bivy. Shelter was a Go Lite Shangri La floorless. Overall, the bag was comfortable to about freezing, after that I had to put on my Kryptek Aquilo down jacket to stay warm in the Hyperion. The construction, compressibility, shoulder room, sleep pad straps, etc are all great, but I think the temp rating is optimistic (though within their “Comfort“/EN rating), at least for me. That’s in no way a criticism because the bag is a beautiful piece of kit, however 20 degrees is probably pushing it if you’re a colder sleeper. This confirmed my belief that there‘s only one way to really find what works for you. Shopping for an ultralight 0 degree bag now. PM if anyone’s interested in the bag. It’ll be properly cleaned and priced fairly.
 
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Justin Crossley

Justin Crossley

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Great observations Tango. Thanks for sharing. I think you're spot on.

If you're a colder sleeper, I would add the Xtherm to your sleep system. I think the pad makes a big difference.

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