REVIEW: Sea to Summit UltraLight Insulated Mat

Looking for a comfy, light, warm and well made air mattress for all your UK backpacking, bikepacking, camping and bivvying needs? Toby Archer thinks he may just have found it.

Air mattresses are hardly a new idea: some of my earliest memories are from 1970s family camping holidays to Spain and my dad standing knee-deep in the Med, first thing in the morning, trying to find a leak in one of our perpetually leaking mats. Camping back then on air mattresses seemed to always involved plenty of sleeping on the ground. Later foam mats were the thing when I started backpacking and still have a lot going for them, particularly for climbers (nothing to puncture), but when Thermarests came along they quickly became popular for offering increased comfort and often less bulk also. Thermarests and later copies are of course also air mattresses, but the air is held in the sponge foam inside the nylon shell of the mat. It is really only in the last decade that the new air mattresses that are open inside have come back to the market – from the likes of Exped, Thermarest, Alpkit and Sea to Summit.

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These air mattresses have a number of advantages, being very light, very compact and often very comfortable as well, but it is not all good news. We get used to thinking of air as the best insulator (well, ok, a vacuum is better but tricky to make into a jacket!) – fluffy down in a sleeping bag or duvet jacket holds air relatively still and this creates the insulating layer between your body warmth and the outside environment.

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The simplest air mattresses hold lots of air, but what you find sleeping on them in cool to cold temperatures is that they do not insulate well. What happens is the temperature difference between your body and the cold ground below produce convection currents inside the chambers of the mat and this circulation soon means heat is being lost from your body. So while open chamber air mattresses are comfy on rough ground they not good at insulating you from the cold ground. I’ve found pure air mattresses to be unpleasantly cold even in temperatures in single digits but still above freezing. Companies have tried different ways to stop the circulation – either complicated interlocking chambers or insulation in open chambers; down or synthetic.

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The Sea to Summit UltraLight Insulated Mat is, as its name suggests, an insulated mat – it uses bonded synthetic fibres in the mat and all the inside is treated to resist the growth of mold. Mold forms because when you blow up an air mat you breathe significant amounts of water-vapour into the mat and it is hard to get it out again. This is why Exped down mats, to take one example, have to be inflated with a pump of some sort - as the down would rot if it got wet. You can get pump bags for the Sea to Summit mats but they claim it is not necessary for the UltraLight Insulated range as it is treated inside to stop mould growing. I have only inflated it by blowing and so far no yuckiness is evident.

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Blowing it up

The first time I blew up this mat I found it was quite hard to get it to inflate – but that was a result of its tight factory packing; ever since it has inflated quickly and surprisingly easily. The valve in particular is an excellent design – it has a double setup, one opens but is one-way making inflation much easier, then the second valve is a bigger opening that allows you to deflate and pack the mat very easily. Having used it recently camping with my family along with a Thermarest and two Alpkit Numos, it was noticeable how easy it was to deflate and pack away the Sea to Summit mat in comparison.

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Warmth and comfort

Once inflated, the mat is very comfy to sleep on: being about 5cm thick it makes even quite bumpy ground into a passable doss. Like many air mattresses, if you plonk down on it just sitting you might displace enough air to literally ‘bottom out’, but that never seems to happen when lying on it as long as it is blown up firmly. In terms of insulation I have been impressed – I slept a night on snow-covered, frozen ground when it was probably about -5 air temperature and it was great.

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"I’d be happy using the UltraLight Insulated Mat throughout the British winter"

Sea to Summit give an R rating to all their mats, as many mat makers now do. This is a measure of insulation, and even if I’m not quite sure how the ratings are derived, they are very helpful in terms of allowing comparison between different mats from different companies. The UltraLight Insulated Mat has an R-rating of 3.3 as opposed to Thermarest Prolight that has one of 2.4 while a closed-cell foam RidgeRest comes in between these two at 2.8. From actual use, I’d be happy using the UltraLight Insulated Mat throughout the British winter. If you were camping extensively on snow or regularly at subzero temperatures, a slightly more insulating mat might be needed (and Sea to Summit have a great range of more insulating alternatives), but this model kept me perfectly warm for one night on snow, while still weighing very little and packing down into a little stuff sack.

Weight and pack size

The UltraLight Insulated Mat weighs 488g (size Regular, on my scales) and packs down pretty small. For its warmth and comfort, the weight seems fair. It's available in three sizes: Small 168x55cm; Medium 183x55cm and Large 198x64cm.

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Noise, cleaning and toughness

The mat is almost silent when you move around on it; I have read other people describing sleeping on some other air mattresses that sound like you are lying on a crisp packet. So it is worth noting Sea to Summit have designed out any annoying noise. Also, even though the mat is made of some form of plastic, it is not unpleasant against the skin. The way the mat is bonded does mean that when inflated it creates a dimpled surface. I’ve found these dimples have a habit of collecting any bits of sand or dirt around and getting them out when inflated is a hassle, but as soon as the mat is deflated and flat it is very easy to wipe clean with a damp cloth.

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I’ve spent over seven nights on the mat now – in temperatures well below freezing to temperatures in the teens. I’ve used it in tents, in a bivvy bag and under a tarp. I always use some sort of groundsheet under it, but have had no problems with punctures so far. Some of Sea to Summit’s more expensive models are actually two separate layers of air chambers, meaning if you got a puncture you still have half the mat's insulation value. With the Ultralight Insulated you don’t have that backup so a puncture would mean you are sleeping on the ground until you can get it fixed (some self-adhesive patches are included with the mat) but that is a risk with virtually all other air mattresses, and with a bit of care and thought about where you pitch your tent or lay out your bivvy bag, it is not a big risk.

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The UltraLight Insulated Mat costs £105 for a size Small, £110 for Regular and £125 for size Large. Comparing it with its most obvious competitors, it is more expensive but slightly lighter and warmer than a Thermarest Prolight of the same length – I have a Prolight and it is a good mat, but the Sea to Summit mat is definitely more comfortable. Perhaps Thermarest’s most obvious competitor is the NeoAir Xlite – with an R rating of 3.2 its is almost as warm as the UltraLight Insulated Mat, but is quite a lot lighter at 353g (183cm long). But then the NeoAir Xlite is more pricey at £130.


Overall the Sea to Summit UltraLight Insulated Mat is great. Yes, you can get lighter, or cheaper, or tougher or warmer mats, but not all of these things in one model. I think the Ultralight Insulated is a great compromise between those four requirements, which makes it a great do everything mat for the UK or similar environments. I haven’t been able to find any downsides to it, so can give it a hearty recommendation if you are looking for an inflatable mat.

Sea to Summit UltraKight Insulated Mat product shot , 104 kb

Sea to Summit say:

The Ultralight sleeping mat has a single layer of medium resolution Air Sprung Cells to give you the lightest and smallest packed volume mat without compromising on comfort. To add warmth, Exkin Platinum is used, a quiet non-woven fabric that reflects radiant heat look back to the user and Thermolite insulation to prevent convective heat loss between your body and the ground. All Sea To Summit sleeping mats come with a quality stuff sack, a repair kit containing six self adhesive patches for repairing punctures in the field, and a spare silicone one-way valve flap.

  • Single layer technology – constructed as a single layer of medium resolution cells
  • 5cm thick
  • R-value 3.3
  • Small: 168 x 55cm Rolled size: 10 x 23cm Weight: 430g Price: £105
  • Regular: 183 x 55cm Rolled size: 10 x 23cm Weight: 480g (Toby says 488g) Price: £110
  • Large: 198 x 64cm Rolled size: 10 x 26cm Weight: 595g Price: £125

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