Therm-a-Rest Hyperion Sleeping Bag Review

Therm-a-rest Hyperion Sleeping Bag Review

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This is a gear review about the Therm-a-Rest Hyperion Sleeping Bags in 2024.

The sleeping bag review covers the whole Therm-a-Rest Hyperion Sleeping Bag Range but I have focused on the Therm-a-Rest Hyperion 20F/-6C which I have extensively tested and reviewed.

All the Therm-a-Rest Hyperion Sleeping Bags use high-quality 900+ Nikwax Hydrophobic down, ultralight 10D fabric on the inner and outer shell, with the outer fabric coated with a DWR. As the lightest sleeping bag in their class, Ultralight Thru-Hikers and Backpackers have a lot of reasons to like the Hyperion sleeping bags.

When it comes to ultralight sleeping bags the Therm-a-Rest Hyperion range has been some of the lightest on the market since its introduction in the spring of 2019. But should you buy it? Keep reading to find out more.

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How We Tested

The Therm-a-Rest Hyperion Sleeping Bag in this review has been extensively evaluated and researched by the expert author who has more than 30 years of experience in Thru-Hiking, Backpacking, and Hiking. He also spent several years managing a hiking retail store and is regarded as an expert in this field. The Sleeping Bag was supplied by the manufacturer for this review. They have been rigorously tested by the author in all kinds of weather on multiple backpacking trips. The research, testing, and experience of the author have combined to present this honest and unbiased review. Read the Review Policy for further details.

Therm-a-Rest Hyperion Sleeping Bag Specifications

Therm-a-Rest Hyperion 20F/-6c Review

Therm-a-Rest Hyperion 20F

Weight: 20 oz / 567 grams
Down Fill Power:
Hyperdry 900 fill
Fill Weight:
11.5 oz / 330 grams
EN / ISO Rated:

> Ultralight
> Very compact
> High-quality down
> Great for back and side sleepers
> Very small internal dimensions can make for a tight fit
> Not the best for stomach sleepers

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Therm-a-Rest Hyperion 32F/0C Review

Weight: 16 oz / 460 grams
Down Fill Power:
Hyperdry 900 fill
Fill Weight:
8.5 oz / 250 grams
EN / ISO Rated:

> Extremely Ultralight
> Smallest Pack Size in Class
> High-quality down
> Great for back and side sleepers
> Very small internal dimensions can make for a tight fit
> Not the best for stomach sleepers

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Therm-a-Rest Hyperion Ultralight Sleeping Bags

The Therm-a-Rest Hyperion was first introduced in the Spring of 2019. The ultralight Therm-a-Rest Hyperion Sleeping Bag range became a success as they chased the ultralight sleeping bag market. Once upon a time, ultralight backpackers and thru-hikers were seen as freaks who compromised durability and safety while chasing lower ounces and grams. Now ultralight is mainstream and accessible to all. The Hyperion range is unashamedly targeted at the backpacker who wants the lightest possible sleeping bag with the highest possible quality.

Therm-a-Rest has seen no need to make any changes since that time as it is still one of the best ultralight sleeping bags on the market.

The temperatures of the bags were independently tested to EN/ISO standards. The sleeping bag standard, ISO 23537, was released as the new sleeping bag standard. The temperature ratings on the Hyperion sleeping bags were tested to this standard. I like this commitment to ensuring the sleeping bag ratings are independently tested rather than a best guess on how warm you should be like some companies do. More on the temperature ratings a little later.

Down type/fill power

The Therm-a-Rest Hyperion Sleeping Bags are filled with 900+ loft Hyperdry Goose Down in 2024. This is the top-of-the-range down used on any Therm-a-Rest Sleeping Bag. It is not only ultra-lightweight but also has good water resistance qualities as it uses Nikwax water repellent down. This means if you are unfortunate enough to find yourself in very bad weather and your sleeping bag gets wet, it will not absorb as much water as other sleeping bags and still be able to loft and keep you warm.


Let’s take a look at how the Therm-a-Rest Hyperion Sleeping Bags are made with features such as the Inner and Outer Shell fabrics, zippers, baffles, draft tubes, hood, and weather resistance.

Outer Shell fabric

The external face fabric of the Therm-a-Rest Hyperion Sleeping Bag is made using a 10-Denier Ripstop Nylon which is coated with a DWR coating to prevent drops of water from entering the bag. Like almost all modern ultralight sleeping bags, the fabric is light and almost see-through, especially when you hold it up to the light.

When testing the Therm-a-Rest Hyperion Sleeping Bags I poured a significant amount of water on the outer fabric to test the water resistance of the fabric and the water beaded nicely and ran off the fabric. More on that later.

Inner fabric

The Therm-a-Rest Hyperion Sleeping Bags use the same 10 Denier fabric that is used on the outer shell minus the DWR coating. It is not only ultralight but also resistant to tearing.

I did the rip test on the fabric by using my hands to try and rip the fabric, even around the stitching area. I was unable to rip it. With a sharp object or knife, I could cut the fabric easily but I don’t want to intentionally destroy this awesome sleeping bag.

Weather resistance

As mentioned above, I did drop quite a bit of water on the outer face fabric to test the water repellency and quality of the DWR coating. I can confirm it will provide a decent level of water resistance that is at least equal to or better than all the competition in the Ultralight Sleeping Bag market.

The Therm-a-Rest Hyperion Sleeping Bag is good enough to sleep outside under the stars when condensation comes down overnight.

Disclaimer: I do not recommend that you pour a whole bottle of water over your sleeping bag to test its water resistance. I do the testing so you know just how good or bad this product is.

Therm-a-rest Hyperion Sleeping Bag water resistant DWR coating
The author testing the DWR and water repellency of the sleeping bag fabric


The Hyperion Sleeping bags use a system of baffles that are a little different from other sleeping bags on the market. While the box baffles are no different from many other sleeping bags, they stuff 70% of the down into the top layer and 30% in the bottom layer. What that means is the layer that is facing down onto the sleeping pad has less insulation and the top layer does all the work of keeping you warm.

In theory, this system is great. But there is one issue. What happens when you roll over at night the 70% of the insulation is on the bottom? Well, if this occurs you will not stay as warm. To combat this, the Hyperion Sleeping Bags have a strap system that they like to call, SynergyLink Connectors that connect the sleeping bag to the sleeping pad and prevent this from happening.

When testing this system I found it to work surprisingly well. Anyone who has used an ultralight backpacking quilt will be familiar with such a system, but sleeping bag owners are not so familiar with such a system. The sleeping bag stayed in place well enough for me to roll around in the bag and not induce the bottom side of the bag with less down to move to the top. While side sleeping the bag turned just enough for me to be very comfortable and not have the hood cover my mouth.

Like most ultralight sleeping bags, I would have liked each baffle to be stuffed with slightly more down. Not like an overfill, but enough to reduce clumping of the down which happens over time and is an indication that the sleeping bag needs a wash. It will need to be done from time to time to keep the bag performing at its best.

The SynergyLink Connectors keep the Thermarest Hyperion Sleeping Bag in place.
The SynergyLink Connectors keep the Therm-a-Rest Hyperion Sleeping Bag in place.

Zips and Draft Tube

The Hyperion sleeping bag series features a 1/2-length zip and a draft tube.

I tried my best to destroy the zip and tried to snag it on the internal draft collar. I was able to snag the zip when I tried but for most people, there is nothing to worry about. There is a bit of a learning curve when it comes to using the zip and locking it in place with the press stud next to the hood. When I say that, the bag is a tight fit and is fiddly to close. After a few attempts, it is not an issue, and after only one night of use, it is easy enough to use.

Overall, the zips and draft tubes do a good job and there is not much that can be faulted. But due to the tight internal dimensions of the Hyperion sleeping bags, I found it could be a challenge to zip up the bag without ensuring I was tucked inside perfectly. With practice, it became easier.

Therm-a-rest Hyperion Sleeping Bag snag free zips
The zip and zip baffle work well


The hood on the Hyperion is good and features a full collar the whole way around. It is a very tight fit and unlike many other sleeping bags, it will not be possible to sleep with your backpacking pillow inside the hood. The hood is just too tight a fit for that. If you use a backpacking pillow it must be outside the hood. This is not a big issue but something you must be aware of. That same compact size of the hood ensures there are not many air pockets that take energy to heat, energy that is better spent keeping you warm.

The Drawcords and toggles used to cinch the hood closed all work as expected and will not be an issue for users.

The neck and hood collars could be a little bigger and could have more overfilled for better heat retention. In my experience the hood collar and neck collar areas of sleeping bags are the first places to get dirty from body oils and sweat which leads to the down becoming more compressed and clumped, making them less efficient at keeping you warm.

When I tested the Therm-a-Rest Hyperion Sleeping Bag I spent a lot of time sleeping on my side and rolling over a lot. The hood worked perfectly and was able to move with me as I turned, even when using the straps to hold the sleeping bag onto the ultralight sleeping pad. I used the Therm-a-Rest Uberlite sleeping pad when testing this sleeping bag. I could find no better ultralight sleeping system than this.

As mentioned above, maybe a bit more overfill in the hood and draft collars would be a good improvement. And I slightly larger fit would be good. But as this is such a niche ultralight bag I am not sure that is something that Therm-a-Rest will ever do as it can only add more weight to the bag.

Therm-a-rest Hyperion Sleeping Bag compact hood

Stuff Sack

The standard Stuff Sack supplied with the Hyperion Sleeping Bags is good and there is no need for anyone to consider upgrading to anything else. It is lightweight and can be compressed with the side straps to compress the bags into a very small size of around 2.5L. The Hyperion is the most compressible sleeping bag in its class of ultralight sleeping bags. Others may come close but this is the best, only ultralight hoodless sleeping bags or backpacking quilts are more compact.


As mentioned above the stuff sac will compress the bag to a smaller size. Refer to the Specification chart for detailed comparisons.


The Therm-a-Rest Hyperion Sleeping Bags are the most packable of all the ultralight sleeping bags in their class. A combination of the high loft down, 10D fabric, and compact zip all contribute to the small pack size.

Therm-a-rest Hyperion Sleeping Bag stuff sack size
Very small pack size of the Therm-a-Rest Hyperion 20F


The internal sizing of the Therm-a-Rest Hyperion Sleeping Bags is on tight size. There is not a lot of room to move around inside compared to other ultralight sleeping bags. There are pros and cons of tight mummy-style sleeping bag sizing.

Although the Hyperion models are classic mummy-style sleeping bags, they have very compact internal dimensions. Their internal dimension is one of the smallest in their class. These compact internal dimensions allow for a greater ability to keep you warm as you waste less energy keeping air pockets warm. As a result, Therm-a-Rest can add less down into the bag and use less fabric in a lighter bag. All of this is a positive when you want an ultralight sleeping bag.

The tight internal dimensions have some negative aspects that need to be highlighted. If you want to wear a winter-grade down jacket while you sleep it will make for a tight fit. This can be a downside if you want to extend the temperature range of the bags during the shoulder seasons. Having said that, they will fit an insulated sleeping bag liner without issue, so that might be a better option for shoulder season travel. If you get cold feet, you could wear a pair of down booties inside the sleeping bag to stay warm.

When I tested the sleeping bag I found that the SynergyLink Connectors did a good job of keeping the sleeping bag facing up. When sleeping on my back the Hyperion Bag was great, perfect. When I rolled over and slept on my side it was surprisingly good. I thought it might cause an issue but it did not.

When I slept on my back, which I tend to do from time to time, I found myself stuck inside the hood. This is my only criticism of this bag just be aware of this. A stomach sleeper will have an issue with this bag. Having said that, most people rarely sleep in their stomach, so for most people, the compact size and ultralight weight will be worth it.

Overall, the Therm-a-Rest Hyperion Sleeping Bags are tight-fitting sleeping bags due to their internal dimensions. If you are overweight, look elsewhere, this bag will not work for you. If you are of average build or smaller then this could be the perfect ultralight sleeping bag.

Side Sleeping in the Therm-a-Rest Hyperion 20F/-6C Sleeping Bag
Side Sleeping in the Therm-a-Rest Hyperion 20F/-6C Sleeping Bag. Note how the bag will still work great when side sleeping


When testing the bag I found the temperature rating to be true to those stated by Therm-a-Rest. Both the Hyperion 20F/-6C and Hyperion 32F/0C sleeping bags have been tested to EN and ISO standards so you can rest assured that the sleeping bag will keep you warm at the temperatures as reported.

I am normally a slightly cold sleeper unless I eat a very heavy meal before going to bed (which can keep you warmer at night). I am a side sleeper in general and I found the bag to work well when sleeping on my side but not so good when sleeping on my back.

It is super important to note that there are 3 temperature ratings listed on each sleeping bag.

The Therm-a-Rest Hyperion Sleeping Bags have the following EN /ISO-approved sleeping bag ratings:

Therm-a-Rest Hyperion 32F/0C Sleeping Bag:

Comfort: 41F/5C
Transition: 32F/0F
Risk: 5F/-15C

Therm-a-Rest Hyperion 20F/-6C Sleeping Bag:

Comfort: 32F/0C
Transition: 20F/-6C
Risk: -9F/-23C

Comfort Rating

The Comfort Rating is the most important rating as this is the temperature at which you will be warm and should sleep well. Unfortunately, the sleeping bag industry as a whole fails to use this rating for marketing reasons. But use this as your base for what bag will keep you warm at what temperature.

This is usually the temperature at which a woman will sleep well without being cold.

Limit Rating

The Limit Rating is used by almost all sleeping bag manufacturers as the temperature rating for the sleeping bag. Few people will get a good night’s sleep at the limit rating unless they know their bodies well enough to know they are warm sleepers.

I know myself well enough to know I am usually halfway between the Comfort and Limit Rating of a certified EN/ISO-tested sleeping bag. This is my rating of how warm I will be at night inside a bag.

This is usually the temperature rating that a male, curled up on his side, will sleep OK. Most people will feel cold and not sleep well when sleeping at the limit rating temperatures.

Extreme Limit

The Extreme Limit is the limit within which people will not die from hypothermia or extreme cold. You can be guaranteed that if you use the bag at the Extreme Limit you will not sleep at all. If going into the Extreme Limit be sure to get a Thermal Sleeping Bag Liner or even better upgrade to a 4 Season Winter Sleeping Bag.

Therm-a-rest Hyperion Sleeping Bag temperature rating


As mentioned above the sleeping bag is relatively comfortable for everyone except when sleeping on your stomach. The internal dimensions of these ultralight sleeping bags are:

Therm-a-Rest Hyperion 20F/-6C:
Length, Width & Height: 80 x 28.8 x 4.5 inches / 203 x 72 x 11.5cm (suitable for a person up to 72 inches 183 cm)
Internal Dimension: 57 x 49.5 x 43 inches / 145 x 126 x 109 cm

Therm-a-Rest Hyperion 32F/0C:
Length, Width & Height: 80 x 28.8 x 4 inches / 203 x 72 x 10cm (suitable for a person up to 72 inches 183 cm)
Internal Dimension: 57 x 49.5 x 43 inches / 145 x 126 x 109 cm

Caring for your Therm-a-Rest Sleeping Bag

When you have a high-quality sleeping bag it is worth taking care to look after it. One of the best things you can do is wear clean backpacking base layers to bed to prevent sweat, dirt, and body oil from penetrating the liner of the sleeping bag. You can also use a sleeping bag liner to keep it clean.

How to store your Therm-a-Rest sleeping bag

The Therm-a-Rest Hyperion comes with a Lofting bag included which is a decent size and certainly good enough to keep a lot of the loft when storing it at home. Compared with other brands it is one of the better lofting bags. I like them big and oversized when storing my sleeping bag.

Therm-a-rest Hyperion Sleeping Bag loft bag

How to wash your Therm-a-Rest Sleeping Bag

Over time the sleeping bag will lose a bit of its loft and you may start to complain that the bag is not as good as it used to be. Down may start to clump together and it might start to have some funky smells that seem to be a cross between a sweaty gym and an unwashed homeless person. If this occurs it is time to wash the sleeping bag.

I wrote an article on how to do this so take a look at How to Wash a Down Sleeping Bag, for further details on how to wash your bag.


The Therm-a-Rest Hyperion series are premium Sleeping Bags at a premium price. Having said that, they sit at the upper end of the premium ultralight sleeping bags market in 2024.

While not cheap, if your goal is to have an ultralight backpacking gear setup then this is one of the best options.

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Therm-a-Rest Hyperion Vs The Rest

How does the Therm-a-Rest Hyperion compare to other Sleeping Bags in the ultralight class in 2024? Check out my full comparison review of the Therm-a-Rest Hyperion and all the Best Ultralight Sleeping Bags 2024.

Best Suited Use

The Therm-a-Rest Hyperion Sleeping Bags would be perfect for anyone who is sleeping in temperatures above freezing or slightly below in the case of the Hyperion 20F/-6C. The following types of trips would be perfect for this bag.

  • Thru-hiking anywhere except on the coldest of trails. If starting early or finishing late on the Appalachian Trail, you could add an insulated sleeping sheet liner and wear clothes to bed. Perfect for ultralight thru hiking on the Pacific Crest Trail.
  • Summer hiking in the Rockies or Sierra in North America with the Hyperion 20F/-6C. Or into the Spring and Fall if using the warmer Hyperion 20F/-6C.
  • Summer hiking in the Alps in Europe or Hiking the Camino in Spain. The warmer bags will be well suited to 3 season trips in most places.
  • Summer hiking and 3-season hiking in Australia and New Zealand in most areas.
  • Summer trips in South America including Patagonia as long as the nighttime temperatures are above freezing. You will need the Hyperion 20F/-6C if heading to the High Andes of Bolivia, Peru, and Ecuador, and maybe even an insulated sleeping bag liner for extra warmth when needed. I tested this bag in the mountains and coastal range of Chile, perfect.


The Therm-a-Rest Hyperion sleeping bags are best suited to anyone wanting a high-quality ultralight sleeping bag. The temperature rating for this bag is true to the specification in my opinion and based on my use of the sleeping bag.

If you want a sleeping bag for the summer months and into the shoulder season for warmer climates then this could be for you. Just make sure you are not overweight or your body is not too large. This is a tight-fitting sleeping bag.

When it comes to improvements, I would like to see the Hyperion sleeping bag increase in the internal dimensions of the bag slightly. Not by much, but by enough so I can use the sleeping bag with a down jacket or puffy jacket and still have a bit of room to roll around. Just 2 inches of internal size increase would make this bag perfect for me. Even though it is not suited for stomach sleepers, I think the compromise of adding less down to the underside of the bag is a great idea to keep the weight down.

Overall, the Therm-a-Rest Hyperion range of sleeping bags is one of the lightest sleeping bags on the market in 2024. There is little to fault and not much that needs improving. Just be very aware that it is a tight fit, so if you are a large person then this may not work for you. If you are an ultralight backpacker or thru-hiker, this could be your next sleeping bag.

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Another one of the Best Backpacking Gear Reviews from BikeHikeSafari.

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Frequently Asked Questions

Are Therm-a-Rest Sleeping Bags any good?

Therm-a-Rest Sleeping Bags are very high quality and ultralight. The Therm-a-Rest Hyperion range is known to be some of the lightest sleeping bags on the market right now.

Does Therm-a-Rest Sleeping Bags use Responsibly Sourced Down?

Yes, All the down sleeping bags from Therm-a-Rest are RDS certified, ethically sourced down that can be traced as responsibly sourced.

Thermarest Hyperion Sleeping Bag Review Pin

BikeHikeSafari Gear Review Process

The author, Brad McCartney from BikeHikeSafari is a small independent adventurer and outdoor gear tester who owns and runs

BikeHikeSafari is not part of a large blog network and is proudly independent. All reviews on this site are independent and honest gear reviews of outdoor products by the author.

The author, Brad McCartney is a very experienced triple crown thru-hiker, adventurer, and bike tourer having spent 1000s of nights sleeping in a tent and sleeping bag (Read more). He was a manager of an outdoor retail store and is very experienced in what is important when using and testing gear for reviews like this.

BikeHikeSafari will never receive any money for reviews and they do not accept sponsored reviews on this website. All the comments about the gear reviews are from the author based on his years of experience. Hope this independent review was helpful for you.

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About the Author:
Brad is an Australian who has completed the hiking Triple Crown after he hiked the Pacific Crest Trail, Continental Divide Trail and Appalachian Trail. He has hiked on every continent (except Antarctica) and has cycled from Alaska to Ecuador. He is an expert on outdoor gear currently living in Chile.

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