Sea to Summit Sleep Systems Review

© Dan Bailey

Note: 'outdoors' photos were taken for illustrative purposes only. No one should be camping or bivvying overnight away from home during Coronavirus lockdown.

I imagine most people tend to buy sleeping bags and mats separately, collecting bits and bobs piecemeal over the years. But for those of us looking to get fully kitted out in one go, Sea to Summit are promoting the idea of a 'sleep system'. The idea, they say, is that you can mix and match a mat and a bag from their extensive range of each, to give you the ideal setup for the intended use. With a sceptical head on - it's my job - that doesn't sound like a 'system' so much as a way to steer the user towards buying both big ticket items from Sea to Summit. But then I can't think of a disadvantage in doing so: this Australian brand does make very decent stuff. And no one's stopping you from purchasing only one item.

It's a thick, comfy mat and a roomy, versatile sleeping bag  © Dan Bailey
It's a thick, comfy mat and a roomy, versatile sleeping bag
© Dan Bailey

We went for a setup well suited to cooler summer nights, and with enough insulation for at least valley use in spring and autumn. With car camping and campsites in mind, we wanted a mat and sleeping bag to offer a bit more comfort than your average lightweight models; but I thought it'd be good if it was all still light and packable enough for occasional less serious backpacking too. Versatile, in other words, rather than ultralight.

Wildlife encounters on a lockdown wilderness camp...  © Dan Bailey
Wildlife encounters on a lockdown wilderness camp...
© Dan Bailey

We opted for the Ascent Ac I, a 750+fp duck down sleeping bag, and the Etherlight XT Insulated mat. Neither could be called light, but both bag and mat are wider than the very tapered mummy designs common in high-end lightweight bedding, suiting the easygoing comfort-oriented brief.

To make it more of a 'system' we also added the inflatable Aeros Pillow, which velcros onto the mat to make your night's sleep that bit more comfy.

Of course Coronavirus put paid to all outdoor plans to date, so my usual in-the-field testing has become in-the-garden - actually quite appropriate to the remit. I hope I've trialled enough different mats and sleeping bags over the years to be able to offer meaningful thoughts, without actually having used them overnight anywhere more challenging than the back yard.

Ascent Ac I Sleeping Bag - £330-£350

As well as having a more relaxed fit than mummy-shaped models, the USP of the Ascent Ac I is versatility, with a multitude of zips that allow the bag to be vented in a number of ways, and even opened out into a quilt. This is great for a bit of campsite luxury, especially in summer, but since it is quite heavy for its warmth, and it's not that warm, I think it is best considered a 2-3 season bag for fairly non-rigorous use. I wouldn't choose it for a weight-critical trip.

It's a nice set for a bit of campsite comfort  © Dan Bailey
It's a nice set for a bit of campsite comfort
© Dan Bailey


A female-specific version is also available, with a right-hand zip that allows it to be joined to the left-hand zip of the unisex model to make a two-person nest for couples (what if you're a same sex couple?). The unisex Ac I comes in two lengths, Regular (max user height 183cm) and Long (max user height 198cm). With the latter you also get more width throughout the bag, and at 183cm tall, but also being fairly broad, I went for Long.

A very wide-fitting bag  © Dan Bailey
A very wide-fitting bag
© Dan Bailey

Loads of room inside  © Dan Bailey
Loads of room inside
© Dan Bailey

Wide in the body, and especially so at the foot end - with a tapered oblong design that's less close fitting than most bags I've used - the Ascent Ac I gives you loads of room to spread out and roll over. I don't think the extra room makes it quite as thermally efficient as a mummy bag of equivalent fill (see below), and if you're being very weight-conscious then the extra space will mean unwanted bulk and weight. But for a comfy night's sleep I really like the unconstricted feel, and I think the cut works particularly well for more casual camping, when you might not want to be trussed up like pigs in blankets.

The hood is quite generously sized, which is good for not feeling too claustrophobic in the night, while the roomy, anatomically cut footbox means less down compression, say Sea to Summit. There's also plenty of space for my size 47 feet - not something I can always say.

Weight and packability

In size Large the Ascent Ac I comes in at 935g (Sea to Summit say 930g). For its rated warmth this is not particularly impressive, since much lighter bags of a similar rating are readily available. Whether that matters depends of course on what you want to do with it. It's no lightweight specialist for alpinism or minimalist backpacking (the Ascent bit of its name being somewhat misleading), but I'd say the Ac I's weight seems very fair for a roomy all-rounder, and it still wouldn't seem over the top for carrying up the occasional hill or three.

Pillow, mat and sleeping bag with a 1L bottle for scale  © Dan Bailey
Pillow, mat and sleeping bag with a 1L bottle for scale
© Dan Bailey

The bag packs into a decent stuff sack, with compression straps that squeeze it down to a nice compact size. This adds a further 66g, so in transit the Ascent Ac I weighs 1001g by my reckoning.

Fill and warmth

This bag uses 750+ fill power 90/10 premium grey duck down, with a dry treatment to help it maintain performance in damp conditions. With a fill weight of 330g in a Regular size bag and 370g in a Long bag, there's a decent amount of fill (though not a remarkable amount given the overall weight of the bag). The higher the fill power, the fluffier the down, and thus the more air it can trap to keep you warm for a given weight of fill. The Ascent Ac I has a nice puffy lofty feel, but while its 750FP is good, it's hardly stellar when models with 800FP or 900FP can be had for similar prices. Sea to Summit's own sleeping bag range runs from a model with 600FP down up to 850+, so in terms of down quality the Ascent Ac is middle of the pack.

So how warm is it?

Every metabolism is of course different, and so too is every situation in which you use a sleeping bag. The variables include absolute temperature, wind, humidity, your state of tiredness, how well fed you are, how vented your tent is, and the quality of your sleeping mat. For this reason the temperature ratings provided by official testing should only be taken as a rough guide, no matter how accurate they may have been in lab conditions.

Bag, mat and pillow get some serious back garden testing  © Dan Bailey
Bag, mat and pillow get some serious back garden testing
© Dan Bailey

Sea to Summit rate the Ascent Ac I as: 2C Comfort, -4C Lower Limit and -21C Extreme, as tested in accordance with the industry standard EN13537. We can instantly discount the Extreme end of the scale; no one wants to flirt with hypothermia or frostbite, and the Ac I is clearly designed for nothing like that sort of cold. According to the test specifications, Comfort is the temperature at which a 'standard' female can expect to sleep comfortably in a relaxed position (women tend to sleep colder than men) while Lower Limit is the temperature at which a standard male can sleep for eight hours in a foetal position without waking. When estimating a bag's warmth as an end user I'd tend to aim somewhere between these figures, but in this case I would suggest erring more cautiously.

As a male who tends to sleep on the warm side I can generally get away with less sleeping bag than a lot of folk. However on a recent garden camping test when the temperature was predicted to drop to low single figures - but certainly not a frost - I tossed and turned in the early hours, feeling borderline chilly inside the bag (dressed in T-shirt, pants and socks, and using the Etherlight XT Insulated mat - see below). On the strength of a few nippy spring nights in the garden in suburban Fife, hardly an extreme environment, I would not want to push the Ascent Ac I below zero towards its official -4 Lower Limit. I'm going to draw the line at that 2C comfort rating.

To protect the all-important core, the bag's vertical chest baffles are said to be better at preventing down from migrating towards the sides of the bag. There's more fill (60%) on top and less (40%) on the underside; this makes sense if you lie on your back but perhaps less so for side sleepers.

Overall I don't think the Ascent Ac I can really be considered that warm for its weight. My suspicion is that being so roomy makes this bag less thermally efficient than a close-fitting model with the same fill would be, and as a result I'd be careful about using it in colder bridge season weather. Save it for more casual valley camping, rather than more rigorous mountain use.


Its 20D nylon fabric, both inside and out, is soft to the touch, not too rustly, and seems easily tough enough for camping. The general build quality also feels high; looked after well, I'd expect this sleeping bag to have a good long life.

With the two side zips, you can open the top of the bag like a flap to ventilate on a warm night   © Dan Bailey
With the two side zips, you can open the top of the bag like a flap to ventilate on a warm night
© Dan Bailey


There's more to say here than for most sleeping bags. You get one drawcord around the head and another across the neck, and the toggles are not too fiddly as these things go. Also included is a very small internal zipped pocket, which is just big enough for a standard sized smartphone (something you want to keep to hand and warm at night for battery conservation). The position of this does feel a bit obtrusive when you roll over.

Most notable is the Ascent Ac I's arrangement of zips. On many bags, especially lighter weight models, the zip does not extend all the way to the bottom. This is fine for saving weight, but in summer you can often end up with hot sweaty legs and no way to ventilate at the foot end. No such issues here. Instead of the standard single zip, Sea to Summit give you three (count 'em).

The bottom zip lets you air your feet without opening the rest up   © Dan Bailey
The bottom zip lets you air your feet without opening the rest up
© Dan Bailey

When it's chilly you obviously do all the zips up, and they have a bit of an internal baffle to keep most of the draught out. But for camping at the milder end of the year you don't always want maximum warmth. On the left, the full-length zip allows you to open right down to the ankles. For additional fresh air for the feet, a short zip at the base of the bag can be opened or closed separately to the main zip; my feet often get hot, so this is a feature I love. A third half-length zip on the right side gives you additional arm movement, and if both side zips are opened part-way the top of the bag can be folded down to get the air in. And if even that much venting is not enough, the whole bag can be opened into a quilt, one side with 60% of the fill and the other with just 40%. This gives you loads of options to suit a range of temperatures.

I love how it opens into a quilt  © Dan Bailey
I love how it opens into a quilt
© Dan Bailey

On a sleeping bag aimed primarily at lightweight backpackers, or alpine climbing, this many zips would be excess weight and faff. But given the Ascent Ac I's more relaxed remit I think this versatile design is a real bonus. It may not be a new innovation in the world of sleeping bag design, but I particularly like the ability to become a quilt.

Sea to Summit say:

The Ascent™ is our sleeping bag of choice for most adventures, most of the time. Offering the perfect backpacking balance of comfort vs weight, our Ascent™ Series sleeping bags have more space than traditional mummy bags, yet still provide the thermal efficiency you need when exploring above the tree-line.

Ascent Ac prod shot

The Free-Flow triple-zip design ensures your sleeping bag retains maximum warmth and efficiency when needed and multiple ventilation options when it's not. The half zip on the right side of the bag provides freedom of movement for both arms, additional ventilation and means the top third of the bag can be folded down as a mini quilt. The full length, two-way left side zip and separate foot zip transforms the bag into a full quilt for when the mercury climbs higher than expected.

If it's warmth you're after, close all the zips, pull the cord locks tight to drag everything in, and relax in luxurious comfort. The generous allocation of high quality 750+ Loft down ensures great insulation, while the oversized draft tubes prevents your body heat escaping. The panelled footbox and 3-dimensional hood make sure you're not compressing the down when you're trying to stay warm. Vertical baffles over the chest section ensure the down insulation cannot migrate or shift to the outside of the bag during sleep, creating cold spots. A side block baffle construction maintains the 60/40 fill ratio, keeping more down on the top of the bag for maximum insulation.

  • Price: £330 Regular £350 Long
  • Weight: Regular: 860g, Long: 930g
  • RDS 90/10 Premium Duck Down
  • Fill Power: ULTRA-DRY Down® 750+ Loft
  • Fabric: 20D Nylon
  • Fill Weight: Regular: 330g, Long: 370g
  • Shape: Tapered Rectangle
  • Temp Rating: EN 2°c Comfort to -4°c Lower

For more info see

Ether Light XT Insulated Mat - £175

As serious outdoor camping mats go, this one is at the big and heavy end of the scale. You can get warmer and far lighter models than the Ether Light XT Insulated. But that bulk equates to a massive depth and loads of room to spread out, so there are big pros as well as obvious cons. If you want one mat for campsite luxury, without also being crazy heavy for chucking in a rucksack to walk up the occasional mountain, then this could be it.

It's mega-comfy, whether you're camping somewhere decent or just in the garden on lockdown  © Dan Bailey
It's mega-comfy, whether you're camping somewhere decent or just in the garden on lockdown
© Dan Bailey


All the mats in Sea to Summit's range have a distinctive construction, a matrix of dot-welded spots that create a series of interconnected air chambers, or Air Sprung Cells.

'Air Sprung Cells operate in the same way as a pocket spring mattress' they say. 'As each cell deforms independently the mattress conforms to your body shape which feels softer and more comfortable with more body contact area and even dispersion of pressure.'

Having reviewed another of the range before, the Comfort Plus Insulated, I think this feature does make for comfy mats. The Etherlight XT Insulated boasts the addition of 'looped baffles', and while I struggle to picture how this looks on the inside, the net result is an extremely thick mat for its weight - literally twice as deep as the Comfort Plus. Its hefty 9cm of depth (Sea to Summit say 10cm) is way more than you get with most backpack-able models, and feels more like a car camping airbed than a skimpy lightweight mat. While a garden lawn isn't a great place to test its comfort on uneven ground, I've tried it laid over several thick books, and the depth of the mat just seems to soak up the bumps. Even side sleepers are going to struggle to feel the ground through this beefy mat. It's a level of campsite luxury I'm not used to.

Its Air Sprung Cells and 10cm depth make this a bit of basecamp luxury  © Dan Bailey
Its Air Sprung Cells and 10cm depth make this a bit of basecamp luxury
© Dan Bailey


So far I think the Ether Light XT Insulated mat has felt warmer than the sleeping bag I've paired with it. This will be thanks to an inner fill that combines synthetic fibres (a mix of hollow ones for warmth and solid ones for durability) with a reflective layer that's designed to minimise radiant heat loss.

R-value is a measure of how effectively something resists conductive heat flow: a bigger R-value means better thermal insulating properties. Most brands now use a common standard for testing R-values, making their figures broadly comparable. The Ether Light XT Insulated mat has a quoted R-value of 3.8. I'd say this makes it warm enough for use year round, though only for less extreme winter cold. By way of comparison the Therm-a-Rest Original Z-Lite, a benchmark mountaineer's closed cell foam mat, has an R-value of 2.2. In a group test of insulated inflatable mats in 2018, the more winter-oriented models we looked at had R-values ranging from 4.4 - 7, so don't expect insulating miracles from the Ether Light XT:

Shape and dimensions

Just like the sleeping bag, this mat is a gradually tapered oblong that offers more room all over than the narrow mummy shape you tend to get with backpacking bedding.

Three sizes are available: Small (168 x 55cm); Regular (183 x 55cm); and Large (198 x 64cm). At 183cm tall I went for Large on the basis that more is the whole point here. I'm fairly broad, and there's loads of room to roll over and spread out. Yes it's excess weight, but again the general feel is relaxed rather than spartan.

At heart it's a big softie  © Dan Bailey
At heart it's a big softie
© Dan Bailey


The Nylon fabric, 30D on top and 40D underneath, feels tough enough to take a bit of abuse. I've found mats like this can be surprisingly robust unless you get them close to sharp rocks; a kit is included here for in-the-field puncture repairs. The fabric is soft to the touch, and doesn't suffer from a crinkly sound - the downfall of some inflatable mattresses.

Weight and packed size

My massive size L mat weighs in at 607g (Sea to Summit say 560g), plus a futher 59g for the stuff sack/pump bag, so in other words its all-in weight in transit is 666g. This is most definitely on the heavy side for a moderately insulated inflatable mat. For instance, at present I am also reviewing a Therm-a-Rest Neo Air XLite. This has an R-value of 4.2 and a weight of just 437g, making it a fair bit warmer and way lighter than the Ether Light XT Insulated mat. On the other hand it's much shorter and more tapered, and notably thinner, so we're not really comparing like for like.

It boils down to intended use. I suspect anyone on an ultralight mission will consider a 600g+ mat a long way over the limit, but for occasional backpackers who are as likely to camp out of the car it doesn't strike me as a deal breaker of a weight to carry in a pack once in a while.

The 'Pumpsack' makes for quick and easy inflation without filling the mat with moisture from your breath  © Dan Bailey
The 'Pumpsack' makes for quick and easy inflation without filling the mat with moisture from your breath
© Dan Bailey

Inflating and deflating

A large and robust two-in-one valve makes inflation and deflation very quick and easy. With an inflatable mat you don't want to introduce moisture into the innards which could encourage mould and mildew growth, so to that end most brands now supply some sort of pump bag. The Pumpsack that comes with the Ether Light XT is cleverly built into the stuff sack, which saves you from forgetting it when packing.

This one is designed to be blown into from a distance (to reduce moisture in the breath). Inflating takes a couple of minutes at most. Roughly four full pumpsacks will inflate the mat, with a few breaths needed at the very end if you want it extra firm.

Sea to Summit say:

Refining lightweight cold-climate sleeping comfort, this mat combines a lightweight 30/40D Nylon fabric, Exkin Platinum® and THERMOLITE® insulation with a loop baffle Air Sprung Cell™ construction to create a 10cm thick mat with an incredibly low weight.

Larger air pockets are created by using many looped TPU baffles which connect the top and bottom fabric layers with our Air Sprung Cell™ dot weld pattern. The looped baffles allow the top and bottom layers to be positioned further apart creating larger pockets of air when inflated that require less fabric overall. Perfect for side sleepers, the extra height of this mat lets hips sink deeper into it without touching the ground.

  • Weight: 607g size L (our weight)
  • R-value: 3.8
  • Dimensions: Small: 168 x 55 cm, Regular: 183 x 55 cm, Large: 198 x 64 cm
  • Thickness: 10cm
  • eXtra Thick (XT) loop baffle Air Sprung Cells™
  • Lightweight, quiet and grippy 30/40D Nylon fabric, field repairable with included self-adhesive patches
  • Exkin Platinum® and THERMOLITE® for insulation
  • Air Sprung Cells™ for a more comfortable sleep
  • Ultra-Fresh® anti-microbial treatment to the TPU formula to prevent internal mould growth
  • Pillow Lock™ attaches an Aeros™ pillow to mat
  • Multi-functional, high flow-rate valve

For more info see

Aeros Premium Pillow - £30-£34

Sea to Summit make a lot of different inflatable pillows, from ultralight ones for backpacking to down-filled ones for winter. In keeping with the ethos of this review, the Aeros Premium Pillow is billed as more of a luxury item for when "you can risk a couple more grams for a great night's sleep".

The pillow fixes in place with velcro pads  © Dan Bailey
The pillow fixes in place with velcro pads
© Dan Bailey

Thick, sculpted and comfy... beats a coiled rope or a folded jacket  © Dan Bailey
Thick, sculpted and comfy... beats a coiled rope or a folded jacket
© Dan Bailey

Having hitherto made do with a rolled up jacket, this is the first inflatable pillow I've ever used. I have to admit to being an instant convert. Improvised camping cushions rarely cut the mustard, and if you want a comfy sleep without losing your pillow halfway through the night then this purpose built version is streets ahead of a stuffsack full of socks or a wodge of damp waterproofs. I've had to fight various family members for the Aeros Pillow on our household lockdown garden camps.

There's not a lot to say about a pillow, but here goes:

Two sizes are available, Regular and Large. I went for Large, because why not. This is pretty big, and actually thicker than my home pillow. Inflated dimensions are: Regular: 34 x 24 x 11cm; Large: 42 x 30 x 13cm.

To hold it into position all night, Sea to Summit give you some little sticky-backed Velcro pads, which fit onto your mat and cling onto the brushed cover of the pillow.

With a slightly scooped shape, and a cutout around the neck, it's really comfy whether you're lying on your back or your side.

It inflates by mouth, via a mini version of Sea to Summit's two-part valve; and it's possible to fine-tune the firmness just by pressing on the 'air in' valve.

Inside is a robust TPU bladder, but the pillow doesn't feel rubbery or sweaty thanks to its brushed polyester outer cover, which is backed by a bit of synthetic fill that helps wick away perspiration. I love the soft feel but I have noticed that some of the stitching on the outer is already unravelling. Perhaps the cat got to it; or maybe the kids.

Squeezing down to the size of a big apple, and weighing just 109g, stuff sack included, it's something I don't think I'd often begrudge adding to my pack for the sake of a more pleasant night. I'll never carry it on a Cuillin bivvy, but I can guarantee it's going to see plenty of wild camping use, whether or not I pair it with its matching Sea to Summit mat.

The RRP of £34 (size L) may be a little steep for what is in effect a sculpted balloon, but it is a pretty nice pillow!

Sea to Summit say:

A luxurious high performance pillow without the weight and bulk. Perfect for travel and camping where you can risk a couple more grams for a great night's sleep. The pillow case construction allows the outer shell to retain maximum softness while still being supported by a high strength TPU bladder.

Aeros pillow prod shot

  • Sizes: Reg, Large
  • Weight: 109g size L stuffsack included (our weight)
  • Brushed 50D polyester stretch knit face fabric for soft hand feel
  • Synthetic fill between pillow case and TPU bladder increases comfort and wicks away perspiration
  • Curved internal baffles create contours that cradle your head
  • Scalloped bottom edge centres pillow over your shoulders whether you are sleeping on your back, side or upright in a chair
  • Featuring our patent pending mini-valve for easy inflate, deflate and fine tuning

For more info see

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28 Apr, 2020

Seems like an ideal set up for canoe or sea kayak trips, where bulk rather than weight tends to be the issue.

28 Apr, 2020

It seems the only part of a sleeping system I'm missing from S2S is a mat, the other things I've got are all comfortable, light, well designed and look like they'll last me years to come.

I've also got a 2 person hammock, which although likely isn't going to be the first choice for most in terms of a sleeping system, (myself included) it packs down to a small water bottle, has ample room for one person and is great for hanging out on nice sunny days.

28 Apr, 2020

I was about to have a good rant about the first three sentences of the review, but then I read the fourth one which did it for me, albeit in an admirably measured way.......

29 Apr, 2020

I know there's always someone who complains about the price of technical gear, so today that's me..

£535 for a sleeping system, i.e. a sleeping bag, SIM and inflatable pillow?

30 Apr, 2020

I think spending that amount would actually keep me up at night..

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