Therm-a-Rest Hyperion 32F/0C Sleeping Bag & NeoAir UberLite Mat Review

Toby Archer sleeps lightly, with a down bag that offers an impressive warmth for its minimal weight and a mat that's billed as the "lightest insulated air mattress available".


Therm-a-Rest's Hyperion 32F/0C sleeping bag and NeoAir UberLite sleeping mat are of course seperate products; you can use the bag with any other mat, or the mat with any other bag, but they are worth discussing together as they show just how good Therm-a-Rest are at making ultralight but still comfortable camping gear.

Bikepacking light with the Hyperion 32 and NeoAir UberLite mat  © Toby Archer
Bikepacking light with the Hyperion 32 and NeoAir UberLite mat
© Toby Archer

Hyperion 32F/0C - £335

This is a top quality goose down-filled mummy sleeping bag, with - as the name suggests - a "transition range limit" of 0 degrees. Its warmth-to-weight is really very impressive.

Therm-a-Rest are using the new ISO 23537 standard for sleeping bag ratings. This has superseded the old EN 13537 system, but from reading up it seems to be basically the same. So the "transition range limit" is what used to be called the "comfort limit" - the lowest temperature where a "standard man" can sleep "in a situation of fighting against cold (posture is curled up inside the sleeping bag), but in thermal equilibrium", i.e. not shivering. I have found with a good number of sleeping bags tested by this method that the comfort limit rating was very accurate for me if wearing socks, a base layer and a light hat.

The mat is thick and the sleeping bag has plenty of loft for its minimal weight  © Toby Archer
The mat is thick and the sleeping bag has plenty of loft for its minimal weight
© Toby Archer

Having tested the Hyperion this summer I haven't yet had a chance to use the bag down to freezing, but I have been comfortable in it sleeping out (no tent, tarp or bivvy bag) at about 5 degrees on a windy night. I trust the rating system, so would happily use the bag if I was expecting a touch of frost.

It is worth noting that the "comfort" rating of the Hyperion 32F/0C is 5 degrees - this is the temperature to which a "standard woman" should be able to sleep comfortably in the bag. Interestingly, the standard woman isn't expected to curl up at all to sleep comfortably at the temperature, unlike the "standard man" at the transition range limit! Related to who can sleep comfortably at what temperature with this bag is that it is available in short, medium and long (168cm, 183cm and 198cm). One size doesn't always fit all, since a small bag has less dead air space to warm up for a smaller person, and a tall person obviously needs to be able to get the hood over their head in order for a bag to work optimally - so it's good to see Therm-a-Rest offering the different sizes.

What makes the Hyperion remarkable is the minimal weight needed to reach that respectable level of warmth - the size medium Hyperion I have weighs just 0.46kg. A few years ago I was very impressed testing the Lightwave Firelight 250 sleeping bag (and it really is a great bag) but that weighs 0.5kg and has a comfort limit of +1 degrees. So Therm-a-Rest have produced a bag that is both 40 grams lighter and very slightly warmer. "What witchcraft is this?" I hear the backpackers out there cry.

Ignore the morning face - I really am enjoying the nice snug-fitting hood!  © Toby Archer
Ignore the morning face - I really am enjoying the nice snug-fitting hood!
© Toby Archer

Firstly, they have used top quality very light materials to make the bag: 900-fill Nikwax Hydrophobic down and 10D Nylon ripstop, both inside and out, although only the outer fabric is treated with a DWR. Inside the bag, the fabric feels silky and comfortable against the skin.

The 0.26kg of 900 fill down is about as good quality as you can get. Whether down neads a hydrophobic coating is something still debated within the industry. Therm-a-Rest, like a number of other companies, think it helps to protect your bag from moisture, while others remain sceptical about how long the treatments last and whether they are worth it. Regardless of your position on the debate, Nikwax is well known for its commitment to sustainability and their down treatment is said to be environmentally friendly (or at least more so than some others). On a related note, Therm-a-Rest use only RDS certified down, meaning it is traceable and comes from down producers who have to meet a set of ethical standards.

Moving beyond top quality materials, design is also important in making the bag so light for its warmth. The bag is box-baffled, not stitched through: this is vital in allowing any bag to work effectively with minimal cold spots, but it's more complicated and expensive to make. Next, and having laid it down next to some other lightweight down bags, it is clear that the Hyperion is a narrower fit, especially in the lower half. I didn't notice this when using it, only when putting it next to other bags, so for me it is perfectly comfortable to sleep in. I definitely move around to some degree when I sleep, but I feel no restriction here. The bag only has a short zip - opening to a bit above my waist when I'm in the bag. This means it can't be opened right out and slept on top of, which perhaps restricts its use in really warm weather - something to consider if you are looking for a sleeping bag to take travelling in the tropics, but not usually an issue in the UK. The hood is effective, but simple, and can close snugly around the face. There isn't a separate neck baffle inside like warmer bags tend to have, but I don't miss this and of course it contributes to the low weight and small pack size.

The 900-fill down is good and lofty  © Toby Archer
The 900-fill down is good and lofty
© Toby Archer

The final design choice made by Therm-a-Rest is what they call "zoned insulation": quite simply 70 percent of the down is in the top of the bag and 30 percent in the base. Holding the bag up to the light on a sunny day, it is really obvious how much less down is in the base. The reasoning here is that no matter what type of mat you use, when you lie on down, you squash it. So the majority of the insulation is over the body where it can loft and insulate, as with a quilt. The only obvious issue with this is if you roll WITH your sleeping bag, rather than IN your sleeping bag. If you roll with it, for example, onto your side, your back is then exposed to the air with less than half the amount of insulation covering your front.

I suspect this is partly why Therm-a-Rest have included what they call "SynergyLink Connectors"; basically two light, elasticated (and detachable) straps that hold your sleeping bag onto your mat. Using the straps means that if you roll during sleep you are far more likely to move in the bag, rather than for the bag to roll with you. This obviously means the zoned insulation works as it should, and although this is the first bag I've used with such straps, I haven't found any disadvantages with the system. The only remote downside I can think of is potentially if you turn to sleep on your side - which I've noticed I do in very cold conditions - you would potentially be breathing into your bag. This is a bit of a no-no as condensation from your breath quickly wets down. But the Hyperion isn't a winter specific bag, and I haven't found this is an issue so far.

Neither takes up much room when packed into their stuff sack  © Toby Archer
Neither takes up much room when packed into their stuff sack
© Toby Archer

Overall the Hyperion 32F/0C is an impressively lightweight bag. There are compromises to get the weight and bulk down that far, but if those are understood then there can't be many 0 degree bags that can compete with it for weight and packed size. The Hyperion's RRP is £335, and whilst that is of course serious money, it is actually quite a reasonable price for a bag this warm and that light.

Therm-a-Rest say:

The Hyperion 32F/0C sleeping bag is among the lightest in its class while still providing high-performance during backcountry pursuits.

The bag uses thermally-efficient box baffled construction in key areas to ensure warmth and comfort in an ultralight package. Designed with high-quality materials and Therm-a-Rest performance features, the Hyperion keeps your pack featherweight without sacrificing an ounce of performance. Storage sack and compression stuff sack included.

  • Fits: Small 168cm Reg 183cm Long 198cm
  • Weight: Small 0.44kg Reg 0.46kg Long 0.52kg
  • EN Comfort 5C
  • EN Limit 0C
  • EN Extreme -15C
  • Shell fabric: 10D Nylon RipStop DWR
  • 900-fill Nikwax Hydrophobic Down™ Stays drier and maintains loft 60 times longer than untreated down
  • Fill weight: Small 0.24kg Reg 0.26kg Long 0.29kg
  • Box Baffled Construction

For more info see thermarest.com

Hyperion 32 prod shot

NeoAir UberLite Mat - £179

The NeoAir UberLite mat is, as the name suggests, ridiculously light for a full length sleeping mat. Indeed it is billed as the "absolute lightest insulated air mattress available", a claim we have no cause to doubt.

The regular size that I have tested is 183cm long (a large is available for the very tall and a short for those shorter in stature or - more likely - the truly weight obsessed who are willing to put their pack under their feet). The regular weighs just 250g and packs down to about the size of a can of pop. It's hard to really get over just how light and compact the UberLite is. For anyone used to a classic Therm-a-Rest of the 1990s or 2000s, even a three quarter length "ultralight" model, it is hard to believe that a packed Uberlite could possibly be a full length mat, let alone one that is 6.4cm thick when inflated.

Being so thick, it is really comfy on lumpy ground   © Toby Archer
Being so thick, it is really comfy on lumpy ground
© Toby Archer

That thickness makes the mat really comfortable. I've bivvied and camped on it on less than perfect surfaces - tussocky moorland in the main - and particularly when you let a little air out from the maximum firmness, it will conform over uneven ground giving you a nice, flat surface to sleep on. Like many modern mats, this one is mummy-shaped. This perhaps accounts for it feeling somewhat narrow. In actual fact at its widest point the UberLite is 51cm wide, exactly the same as width as a Therm-a-Rest Ridgerest or Z-Lite, which (owning one of each) I tend to think of as the standard for a "full width" mat. So two UberLites next to each other would need the same width in a two man tent as two RidgeRests would, even if there would be spare space at the foot end. I find with shaped mats it is possible for your feet to slip off the narrower end but, particularly when it is cold, I seem to have developed the ability to notice this and move my feet back onto the mat without really waking up.

The UberLite is not a simple air mattress. Therm-a-Rest have developed a bonding technology that allows them to make an air mattress of multiple interconnected chambers that, in cross-section, would resemble two layers of interlocking triangles. Although ultimately all these chambers are connected to each other - all the inflation is done through one valve - they stop the convection currents from being able to form within the mattress. This construction should give the UberLite the edge over open chamber air mattresses in terms of insulation. The simple construction of open chamber mats does allow them to be both very light and much cheaper than the pricey UberLite with its RRP of £179, but that high price will reflect the UberLite's insulation value.

Therm-a-Rest do not claim the UberLite to be a year-round mat. They give it an R rating for thermal resistance of 2, compared to 2.8 for the aforementioned RidgeRest or 2.5 for a Thermarest ProLite - pretty much the "standard" 2.5 cm thick self inflating Therm-a-Rest.

Hyperion 32F & NeoAir UberLite Mat on a Peak District tarping trip  © Toby Archer
Hyperion 32F & NeoAir UberLite Mat on a Peak District tarping trip
© Toby Archer

The sleeping bag and mat (top, centre) don't take up much pack space!  © Toby Archer
The sleeping bag and mat (top, centre) don't take up much pack space!
© Toby Archer

The UberLite arrived for review in early summer so I haven't had an opportunity to try it in cold conditions. The coldest air temperature I've used it in was around 5 degrees. I was warm and comfortable that night, but what is under your mat is as important to its insulation. On that cool night I was sleeping on dry, tussocky grass and heather - which offer some insulation from cold ground itself. No wonder the mat felt warm. I've also used it on flat, sheep-cropped grass after days of rain and cool weather meant the ground was wet and cool. The air temperature might have been a bit warmer than the 5 degree night, but damp cool ground will test a mat's insulation value much more, and here the UberLite felt just as warm. I wouldn't take it if I knew I was going to be sleeping on snow or frosty ground, but my sense so far is that it is warm enough for UK three season conditions.

The material it is made from, "15D rip nylon", feels incredibly light and the mat comes with a lightweight repair kit and instructions on how to use it. Nevertheless, I've had no punctures despite treating it "robustly" for review purposes - for example bivvying with it without using my Tyvek ground sheet which I normally would do. Therm-a-Rest have a video of a Jeep driving over the UberLite and it doesn't pop so the seams are well bonded, although this isn't a test I felt a need to repeat! The mat comes with a little stuff sack to protect it when rolled up and shoved into your pack.

A mat this deep is comfy even on very lumpy ground  © Toby Archer
A mat this deep is comfy even on very lumpy ground
© Toby Archer

The nylon of the mat isn't the nicest feeling material against skin, but no better or worse than most other mats. The UberLite isn't a noisy mat, something that was said of some of the brand's earlier air mattresses. It hardly seems to pick up any dirt, but can be easily wiped off with a damp cloth if need be.

I believe that Therm-a-Rest are introducing new valves across the range next year, but the UberLite comes with a valve that looks pretty much like the one on my 1991 model! "If it ain't broke, then don't fix it" comes to mind here and for inflation it works perfectly but for deflation (and you really need to get all the air out to get it to roll up into its stuff sack) the valve doesn't work nearly as well as the double valves as used by, for example, Sea to Summit. Deflating and rolling up the mat, whilst hardly an epic task, takes longer and more care than my Sea to Summit Ultralight Insulated mat requires.

Blowing the UberLite up takes me about 15 - 20 deep breaths, enough to make you a bit dizzy if you try to do it quickly! You also definitely can see droplets of water inside the mat after blowing it up - a mix of saliva and moisture in your breath. My mat has no mould in it from this, but presumably it is a potential issue - although with no insulation in there, not necessarily a problem. Therm-a-Rest do make a pump sack and even a mini electric pump that would get round this issue, but obviously at extra weight and cost. Some of the moisture must evaporate and come out when you deflate the UberLite, as it doesn't seem that moisture is building up inside, so perhaps seeing the odd drop of liquid in your mat is more of a quirk than a failing.

Overall the UberLite is an incredibly light camping mat that is very comfy despite the lack of weight. It won't be the best for winter camping (at least, not without using it in conjunction with a foam mat) and it is very expensive. But the UberLite is surprisingly robust for its minimal weight and you have the back-up of Therm-a-Rest's excellent reputation for making long lasting equipment and exemplary customer care if there is any fault in the manufacture.

Therm-a-Rest say:

As the absolute lightest insulated air mattress available, the UberLite keeps your pack featherweight on the trail.

Our proprietary construction provides the critical warmth needed in the backcountry. Boasting 2.5 inches of our legendary NeoAir comfort, the minimal UberLite makes a big impact during nights in the backcountry. To endure the rigors of the backcountry, our unique fabrics and construction meet our strict durability standards. Stuff sack and repair kit included.

  • R-value: 2
  • Weight: Small 0.17kg Reg 0.25kg Long 0.34kg
  • Length: Small 119cm Reg 183cm Long 196cm
  • Thickness: 6.4cm
  • Top fabric: 15D rip nylon
  • Bottom fabric: 15D nylon
  • Shrinks down smaller than any NeoAir® ever
  • Reliable NeoAir® Construction: Compresses small enough to fit into your pocket with the included stuff sack

For more info see thermarest.com

NeoAir Uberlite prod shot

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