Review: Rab Ionosphere 5.5 Sleeping Mat

Rab’s Ionosphere 5.5 guarantees a warm, comfortable and quiet night for alpine bivies and camping in extreme conditions

Feature type Review

Read time 7 mins

Published Oct 04, 2023

Photographer Sam Grosvenor

Hannah Mitchell BASE Digital Writer Hannah is a Lake District-based journalist and all-round outdoor lass with a particular fondness for rock faces.


Incredibly warm, impressively comfortable and thankfully, very quiet. The Ionosphere 5.5 is the perfect 4-season partner for the light-sleeping alpinist!

Weight 690g (Regular)
Dimensions 183 X 51cm
Packed size 24cm x 12cm
R Value 5.5
Features Stratus™ R 100% recycled polyester 200gsm insulation with TILT reflective film, 20D Recycled Polyester outer and fluorocarbon free DWR


  • Oversized outer chambers keep you in the middle of the mat
  • Grip print helps reduce sleeping bag slippage
  • Rectangular shape is comfortable for side sleepers
  • Compact pack size but generous 8cm depth
  • Super warm even when sleeping on ice


  • If I had to nit-pick, lighter mats may be available at comparative price points


I’ve been venturing into more extreme conditions of late. Scottish winter was the gateway drug, and now I’m craving higher peaks, bigger challenges and colder temperatures. But with this new-found appetite for altitude comes a need for more technical kit. And with that, I’ve got a dilemma.

I know all to well how heavily the textile industry contributes to greenhouse gas emissions. Then there’s PFAS, greenwashing, end-of-life solutions… it’s really tricky to justify a selfish desire to have decent kit that’ll keep me safe and comfy in the outdoors, whilst claiming to care about protecting the outdoors too. It’s an issue that Rab seem to be acutely aware of and making some really promising efforts to address – in particular, the recent launch of their Material Facts labelling initiative, which aims to eradicate the use of confusing language like eco and sustainable, and replace them with cold, hard facts and data like the percentage of recycled materials used, fluorocarbon content and country of origin of their gear. This is currently available for all new clothing and sleeping bags, with plans to develop this across their remaining gear. Rab are certainly one of the small number of brands who seem to be making honest progress, rather than false promises, and for that I’m willing to buy in.

Back to my more physical needs: I’m after a sleeping mat that’s going to keep me warm in minus temps. With alpine bivies on the cards, it needs to be relatively light and pack down small. It needs a high R value, a decent amount of durability against abrasion and because I will wake up to the sound of gnat’s fart even when sleeping in my own bedroom, it needs to be squeak, rustle and slip-free. I’m a side sleeper too, so I need a shape that accommodates that.


It’s pretty wee, all packed up in its stuff sack. I’m pretty happy with how much space it’ll take up in my pack. In hand, there’s some weight to it, but not a concerning amount. The material feels tough but smooth, with a little bit of grip on the upper side.

The material feels tough but smooth, with a little bit of grip on the upper side

Inside the sack, there’s also a puncture repair kit and an inflation bag. On the subject of which: I defy ANYONE to use this inflation bag and not smile. Go on. It’s adorable. My past experience with inflatable mats is that they tend to feel like sleeping on a whoopee cushion, squeaky and squashy in a way that is definitely NOT conducive to a good night’s kip, so I give the mat a quick lie-down test on my living room floor. Not a squeak – this is promising!

The inflation process is straightforward – you just open the bag up, attach it to the non-return part of the two-way valve system, roll and clip it closed it like a dry bag and squeeze. I count four-and-a-bit Elephants of inflation (which should henceforth be the official measurement for Rab mat inflation, IMO).


The main test for the Ionosphere 5.5 was a night bivying on the glacier beneath the Dent du Géant (or Dente del Gigante, in Italian) in the Mont Blanc massif. The approach to our bivy spot was a relatively short glacier crossing from the Rifugio Torino. My pack felt very reasonable weight-wise, and the cylindrical pack shape of the Ionosphere 5.5 squashes easily alongside your less malleable items! Having dug out our pit for the night, we feasted on freeze dried goods before heading for bed. For the real gear geeks among you, my full sleep setup includes Rab’s women’s Alpine 400 Down Sleeping Bag and Alpine Bivy – combined with the Ionosphere, I was feeling rather smug about my very cosy looking quarters.

Now, anyone who has slept on a glacier before will know that it isn’t always an especially restorative experience. Inevitably I tossed and turned a bit, but never seemed to find the edge of the mat nor slip a great distance in any direction on it owing to the oversized outer chambers and grippy print on the outer. The insulation in this mat is really something; whilst it was a relatively warm night with temps dropping to around 3°C, lying on my side, there was a marked temperature difference between the side of me that was against the mat vs the one facing the open air. Oh, and even with all the moving around, the mat barely made a sound, so my companions were still on good terms with me by the morning.

In terms of comfort – the Ionosphere is unrivalled by any mat I’ve ever slept on before. When camping or bivying, I’m quite prone to getting hotspots or achey bits around my hips, but this night? Nada! For a side sleeper, you couldn’t really ask for much more.

lying on my side, there was a marked temperature difference between the side of me that was against the mat vs the one facing the open air


The Ionosphere 5.5 is the warmest mat in Rab’s range, and the price point reflects that. For those looking for a summer-shoulder season camping mat, this one would probably be overkill. If you’re looking for something for more technical mountain adventures in colder temperatures that handles rock, snow and ice with ease, the Ionosphere 5.5 is likely to provide a long-lasting return on your investment.

Size-wise, the Ionosphere 5.5 is well suited to those with limited space in their pack, and whilst I’ve heard whispers that there are lighter mats available at a similar price point, I can’t imagine that they offer the combined insulation technology and thoughtful design that this one does, and personally, I’ll gladly take a little extra weight for a better night’s sleep. To conclude: this one’s for mountaineers and alpinists who value a decent kip, and equally for those who value environmental transparency.



The Ionosphere 5.5 utilises both radiation and convection to reduce heat loss, with heat-reflective TILT technology and air-trapping Stratus™ R insulation. Try it out on ice – it’s really impressive!


As a light sleeper, I feel seen by Rab’s design team. The baffle design, grip print and quiet construction all mean I can thrash about without ending up on the ground, or with no friends.


Maybe this is subjective, but I’m more than happy with both the size and weight of the Ionosphere 5.5, particularly considering the comfort and warmth it offers.


Value for money is always subjective – but you probably wouldn’t be here if you weren’t in the market for a mat of this kind. It feels robust enough to have a good lifespan – keep your crampons well away and I’d say that this mat will give you many, many years of warmth and comfort. Again, if you’re after something a little lighter on your pocket or perhaps don’t need such a high R value, you might consider something more like the Stratosphere 4. I will happily use the Ionosphere 5.5 for summer camping too, just with a lighter, synthetic sleeping bag, and because I’m content with its weight and pack size, I don’t feel the need to have multiple mat options.

For my needs, the Ionosphere 5.5 does a brilliant job of balancing out weight and pack size with warmth and comfort, so is worthy of its price tag.


Like layering systems, finding the perfect sleep setup is a fine art. For the scenario in which this mat was tested, it performs like a dream, and I have no doubt that it would continue to do so in much colder temperatures too. If you’re a back sleeper, you might find you save a few grams with a mummy-shaped mat, but for side sleepers, you’re going to want to try this one. The thickness of the mat is a real selling point for me, the beefy 8cm depth keeps you well away from lumps and bumps so you can comfortably kip. Rab’s environmental credentials and transparency tick a box for me too, and if you’re into that sort of thing (and let’s be honest, we all should be), the recycled content used in the insulation and main material of this mat is noteworthy.

For relative newcomers to the sleeping mat market, Rab have created a really strong, quality offering and a range to suit most budgets and activity levels.

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