When it comes to staying warm on a winter camp or an alpine bivvy, a toasty sleeping bag is only part of the story. Because the bag's insulation will compress under you, the quality of what goes between that and the cold, hard ground is pivotal. A decent insulated mat can make all the difference to your comfort - and conceivably even your safety on a mountain night. The modern breed of insulated, inflatable mats offer plenty of warmth for minimal weight and pack size - and as with sleeping bags, a down fill is the gold standard in terms of both insulation and packability.
Mountain Equipment's new Aerostat Down 7.0 has to be one of the warmest mats on the market - and thus one of the best for use in cold conditions. I've had a pre-production sample on test for the last year, and while the version now in the shops is a little different, the change is unseen within. My mat has 120g of 90-10 700 fill power duck down inside, held in place in a series of helix-shaped baffles; however the version now available boasts a more generous 180g (size Regular). As far as I can establish, that's more down than you'll find in any alternative model.
This is a high quality, state of the art mat which fully justifies its price tag. I've used mine a lot over the last 12 months, so it's nice to be able to provide a long-term verdict on what, I think, is a really great product.
Clearly I have a less-insulated prototype, but even this is impressively warm. Camping on deep snow last winter, on a night that went down to at least -8, I was plenty snug enough. Having a decent bag helped, but it was noticeable too how little cold I felt from the ground below, even when sitting up on the mat (something that normally brings you closer to the cold). And having slept on it on several more sub-zero nights since then, I've no doubt that this is a mat you could rely on to take you down to very low temperatures indeed - think Alpine winter, high altitude expeditions or polar shenanigans.
I'm unlikely to be doing any of the above for the forseeable future, but even for UK winter use I think a mega-insulating mat comes in handy. The modest extra weight in your pack compared with a less-insulated alternative could in theory be compensated for by needing a rather less warm sleeping bag. Besides, how often do you worry about being too warm when camping in the winter hills?
For the production version, with that 180g of down, ME's 'good night's sleep' temperature is a frigid -40!
But if you want something more scientific than an anecdotal 'it's toasty', the Aerostat also has an R-value of 5.0. While it can't tell you everything, an R-value does provide a useful objective indication of insulating performance, and serves as a quick way to compare different models. This is a lab-based measure of how effectively something resists conductive heat flow: a bigger R-value means better thermal insulating properties. Until recently there was no industry standard test for mats, and it was unclear to us end users exactly what the various rival brands were basing their R-value figures on. ME held back the the Aerostat mat until a new test came on stream.
ME's Product Engineer Matthew Fuller tells us:
"We are relaunching our Aerostat sleeping mats to coincide with the publishing of a Standard method for testing sleeping mats, ASTM F3340. The Standard is there to measure the R value of a mat, which represents how well the mat insulates you from the ground and therefore how warm the mat feels. Having a Standard test is a positive move for the industry, levelling the playing field between brands and making it clearer for consumers.
"Lab tests like ASTM F3340 are an essential part of our development work but they play second fiddle to our user testing, which reveals a lot more about a mat's performance than just one number – the R value – does. Our mats have been very thoroughly field tested with our pro partners and friends of the brand traversing Greenland, sleeping in Alaska at -40 °C, and using the mats throughout the Greater Ranges. While a Standard lab test to assess warmth is a good move forward, it will never be a substitute for real life user feedback."
With its deep baffles, this is a very supportive and comfortable mat. I've found it soaks up a lot of the bumps on uneven ground, so even if it's a poor pitch I've managed a decent night. I tend to sleep on my side, and the vertically-aligned baffles are great for this (versus ridges that run cross-ways). The ripstop fabric has a matt texture that doesn't slip too much on a shiny groundsheet, too.
Does it perform in damp conditions?
In a word, yes. Initially sceptical of using a down-filled mat in wet weather and temperatures above zero, I bit the bullet one horribly humid and rainy night back in the summer. The inner of my tent was soaked in a downpour as I struggled to put it up in the dark, and though I mopped up the puddles as best I could it was still a decidedly damp groundsheet on which to roll out a mat. It proceded to pour all night, and the already-saturated inner tent dripped liberally. Come morning (and it couldn't come soon enough) the mat still seemed fine, and its outer fabric hadn't visibly absorbed any water. Furthermore, the 30 denier laminated ripstop nylon fabric is really tough stuff; I've never yet worried about accidental punctures (something of an issue with some lightweight air mats, in my experience).
Shape and dimensions
Aerostat mats come in a choice of Short, Regular, Long and Wide Regular. I have a Regular. At about 185x54cm this is a large mat. Its oblong shape might cost you a bit of extra weight versus a tapered mummy-shaped mat, but on the plus side it gives you a bit more usable sleeping area. If you're out for a few nights then these generous dimensions will come in welcome. A depth of around 7cm makes this one of the thicker mats I've used, which again just seems to help with the sense of comfort. Mountain Equipment haven't skimped any here.
Weight and pack size
My sample size Reg mat weighs 626g, plus a further 64g for the stuffsack/pump. While the production version is slightly heavier owing to the extra down fill, its official figure of 735g still compares well with other insulated mats. The weight also includes the stuffsack/pump, something that not all brands will account for in their headline figure.
The Exped Downmat HL Winter that we looked at in our 2018 mats group test is perhaps the nearest eqivalent to the Aerostat Down; in size Regular that weighs 557g all-in but it has a narrower, tapered shape and so even this is not directly comparable. For its warmth and comfort, generous size and general robustness, I couldn't possibly quibble at the Aerostat's weight.
When packed away mine rolls into a bundle about about 25cm long - bigger than some insulated inflatable mats, but by no means massive considering what's inside.
Inflating and deflating
Using a design patented by Exped, the Aerostat's 2-in-1 valve is effective and robust. So far there's been no sign of leaks through this valve (neither air nor down).
With its down fill in mind, it's obviously important not to introduce moisture into the mat by blowing it up directly at the valve. Instead Mountain Equipment have provided their own take on the inflating bag, the Windsock. Cleverly incorporated into the mat's stuff sack so that it never gets lost, this is a long sleeve which connects to the intake valve at one end, and seals with a rolltop closure at the other.
The idea is to blow into the open end, from a distance of at least 20cm to reduce the moisture content, then seal the end and squeeze the air into the mat. It takes at most a couple of minutes to fill the mat, and because the sleeve is smaller than some (Exped's for instance) you're looking at six or seven sock-fulls.
Some mats are a bit of a pain to deflate, but when it comes to squeezing the air out of the Aerostat mat, the large open hole at the valve makes rolling it away very quick and easy.
Robust, comfortable, quick to inflate and very very warm, the Aerostat 7.0 is a serious mat for seriously cold places, but one that'd still be worth having in the British hills too. I am enough of a gear geek to get excited by camping mats, and having tried more than my fair share over the years I'd say this is almost certainly the warmest winter-worthy model currently out there.
Mountain Equipment say:
A down filled sleeping mat that gives exceptional insulation and comfort with a small pack size. Combining Exped® patented construction and a unique internal Helix technology the Aerostat 7.0 Down mat is suitable for serious cold weather use. Robust welding and durable 30 denier Nylon ripstop fabric ensure long term expedition performance. A custom valve combines inflation and deflation and the supplied stuff sack doubles as a pump.
- Price: £170
- Weight: 735g (including stuff sack)
- Sizes: Short, Regular, Long
- Dimensions: W 54cm, L 170/185/200cm, D 7cm
- Good night's sleep: -40
- R-Value: 5.0
- 180g (Reg) of 90-10 Pure Duck Down with a minimum fill power of 700
- Vertically aligned baffles with Helix technology to reduce down migration
- 30D ripstop nylon with TPU lamination
- 2-way self-sealing Gas Mask valve for inflation and deflation
- Supplied Windsock™ inflates mat easily and doubles as lightweight stuff sack
For more info see mountain-equipment.co.uk