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By: Andrew Forrest - September 2025
R-values: What they are, what they mean, and why they matter. Being familiar with R-values will help you choose the right sleeping mat for a great night's sleep in the great outdoors, and this guide will explain all you need to know.
At Walks4all, we've noticed a lot of confusion around sleeping mat R-values. If you've ever wondered 'What R-value sleeping mat do I need for camping in the UK?" or been baffled by the numbers on a mat's spec sheet, in this article, we'll clarify what R-value means, why it matters for your warmth, and how to choose the right R-value for different UK seasons (summer, 3-season and winter).
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Understanding R-values will help you select the best sleeping mat for comfortable nights outdoors, so you can avoid shivering on cold ground during overnight camps and avoid lugging unnecessary extra insulation on warm summer nights.
By the end, you'll know exactly how to interpret R-value ratings and pick a mat that's just right for your adventures, whether it's a
lightweight summer hike or a frosty mountain bivvy.
Treat R-values as your mat's floor-warmth setting. It is a single, cross-brand number that boils complicated materials and construction down to how effectively the sleeping or sit mat shields you from the ground.
Pick the R that matches the coldest night you realistically expect, then choose the mat style that achieves it; this cuts through thickness, fill and marketing jargon. In practice: I always set the R first, and let weight, comfort and pack size be the fine-tuning.
In simple terms, an R-value is a measure of how well a material resists heat loss. The higher the number, the better it insulates. The 'R' stands for thermal resistance. For sleeping mats, and similarly for some sit mats, a higher R-value means the mat is better at preventing your body heat from seeping through to the ground. It provides a standardised way to compare the warmth of different mats regardless of their construction.
If you place a sleeping mat between your body and the cold ground, the mat's R-value indicates how effectively it can block the transfer of
your body heat to the ground. A mat with an R-value of 1.0 provides only basic insulation, which is generally fine for warm summer nights,
whereas an R-value of 4 or 5 means the mat can insulate you even on frozen winter ground.
In practice, most camping mats have R-values ranging from about 1 (minimal insulation) up to 8 or more (extremely insulated for high-altitude or arctic conditions). In other words, the higher the R-value, the warmer the mat is.
Importantly, R-values are additive and are separate from the mat's thickness or comfort rating. It's a scientific measure of insulation, not cushioning. You can even combine two mats, and their R values will add together. For example, an inflatable mat with an R-value of 4 placed on top of a closed-cell foam mat with an R-value of 2 yields a total R-value of approximately 6.
We'll discuss tips like stacking mats later on. For now, remember that R-value is one of the most crucial specs when choosing a sleeping mat for the conditions you expect - it tells you how well that mat will keep ground chill from affecting you.
When camping, the ground is often the primary source of heat loss. While your sleeping bag insulates you from the cold air, the part of the bag underneath gets compressed and loses its loft, thereby significantly reducing its insulating ability. Without a good insulating mat beneath, your body heat will quickly conduct into the cold ground, leaving you chilly from below even if the air temperature and sleeping bag feel warm above.
Even on a mild night, the earth is usually cooler than the air, so it will steal warmth from your body unless a mat slows that heat transfer.
On a truly cold or frosty night, having a low R-value mat can lead to a long, miserable bout of shivering, or worse, potential hypothermia if
the ground is cold. That's why, at Walks4all, we always emphasise picking a mat with suitable insulation for the coldest conditions you'll face.
In fact, many people who 'sleep cold' in a winter-rated sleeping bag eventually discover the culprit is an inadequate mat, not the sleeping bag itself.
In short, R-value matters because it's your defence against the cold, hard ground. A properly insulated sleeping mat can make the difference between a comfortable night's sleep and a night spent awake and freezing.
Along with your sleeping bag and sleeping bag liner, they all form your essential sleeping system, and it's a key piece of gear for year-round camping comfort. It is arguably just as important as the temperature rating of your sleeping bag in determining how warm you feel at night, as a sleeping bag only works when paired with enough insulation underneath you.
The complete sleep system - a sleeping mat, a sleeping bag and a sleeping bag liner
In the UK, we generally talk about three broad camping 'seasons' for gear: summer, 3-season (spring, summer & autumn), and winter. Each has typical nighttime temperature ranges and corresponding needs for sleeping mat insulation. Use the table below as a general UK seasonal R-value guide:
| Season | Typical night temperatures | Recommended R-value range |
| Summer (Jun-Aug) | ~5°C to 15°C (cool nights, no frost) | R 1 to 1.5 (minimal insulation for warm weather) |
| 3-Season (Spring/Autumn) | ~0°C to 5°C (frost possible at night) | R 2 to 4 (moderate insulation for chilly nights) |
| Winter (Dec-Feb) | ~-5°C to 0°C (regular frost, some snow) | R 4 to 5+ (high insulation for subfreezing conditions) |
For extreme cold winters or when camping at high altitudes, where temperatures can drop below -10°C, aim for R6 or higher, or plan to
stack mats to achieve this level of insulation.
If you are generally a cold sleeper, which we will discuss later, I suggest adding one to all the above numbers. For example, for a 3-season mat, choose R3-5 rather than R2-4.
If in doubt, err on the side of a higher R-value, especially in the UK, where the weather can be unpredictable. A slightly 'warmer' (higher R) mat will not make you too hot in summer, but having too low an R-value in cold weather can ruin a trip.
I generally use two mats, a very lightweight one with a low R-value for summer, and a higher R-value mat for the rest of the year. I generally
combine this with a closed-cell foam mat that I attach to the outside of my
backpack.
It serves two purposes - I obtain a higher R-value, and it protects my air mats from punctures.
For specific product suggestions, check out our Best Sleeping Mats article, where we highlight top-rated mats for summer, 3-season, and winter use, along with a detailed guide on the factors to consider when choosing a sleeping mat - comfort & thickness, insulation & warmth (R-value), surface texture, durability & materials, size & shape, weight & packability, ease of inflation and deflation and how to balance these for an optimal camping experience.
Sit mats, the shorter sibling of the sleeping mats, sometimes also have R-Values. We have outlined what you need to consider when purchasing sit mats in our Sit Mats guide. If you are just outdoors for the day, sit mats make a useful addition to any hike, outdoor event, or festival - basically anywhere where you may want to sit and keep your bum dry and warm.
Always consider your personal comfort profile: if you know you run cold at night, opt for a higher R-value than the minimum suggested for the temperature.
Every person is different. Two campers on the same night might have very different comfort experiences with the same sleeping mat. Here are
some personal factors to consider when choosing the right R-value for you:
Some people naturally 'sleep cold', meaning they feel chilly at night even when others are warm. If you often find yourself cold at night or have poor circulation, count yourself as a cold sleeper and choose a higher R-value than the bare minimum for the expected temperature.
Women often fall into this category; on average, women tend to get cold more easily than men at night due to factors like lower body mass and hormonal differences.
Your body mass and composition influence how much insulation you need. A smaller or leaner person has less body heat to spare and can get chilled faster, so they may prefer a higher R-value to stay comfortable.
Conversely, a larger person might have a bit more thermal mass and often sleeps slightly warmer. But if you are heavy, you also compress air mats more, potentially reducing their effective insulation at pressure points.
If you have a larger build (like me) or broad shoulders, ensure your mat is thick/insulated enough that you don't 'bottom out' (compress it completely) under your hips or shoulders. Side by side, a heavier camper might opt for a higher R-value or a thicker mat than a lightweight camper to achieve the same temperature, ensuring no cold spots.
How you sleep can make a difference in perceived warmth. Side sleepers, for example, concentrate their body weight on a smaller area (hip and shoulder), and tend to compress their sleeping pad more at those points. This can lead to cold spots if the mat isn't insulated enough or thick enough. A side sleeper generally benefits from a slightly higher R-value and a thicker pad compared to a back sleeper in the same conditions.
If you sleep on your back or stomach, your weight is more spread out, and you might get by with a lower R-value more comfortably than a dedicated side sleeper. Also, if you toss and turn a lot at night, consider a pad with a slightly higher R-value and perhaps a larger size to ensure you stay on it and warm despite moving around.
People with a fast metabolism often generate more body heat and might stay warmer more easily. In contrast, those with a slower metabolism or certain medical conditions may feel colder more easily.
If you know you're the type who always wears an extra layer to bed, plan for a higher R-value. Age can also play a role, as we often feel the cold more intensely as we age. Therefore, an older camper might choose a warmer pad than a younger camper in identical conditions.
Even diet and hydration can affect how warm you feel.
For many years, different gear companies tested and reported R-values using their own in-house methods. This made it tricky to compare one brand's mat to another - an 'R5' from Brand A might not equate to the same warmth as an 'R5' from Brand B.
Fortunately, since around 2019/2020, the outdoor industry has widely adopted a unified test procedure for R-value, so ratings are now consistent across most major brands.
The standard is known as ASTM F3340-18, developed by ASTM International in collaboration with leading outdoor companies.
ASTM F3340 is the industry's standard laboratory method for measuring the R-value of sleeping mats using a guarded hot-plate setup under compression. ASTM announced it on November 19, 2018; the current active edition is F3340-22, published in 2022. Brands began labelling pads to the standard during 2019-2020.
ASTM is a voluntary standards body (founded in 1898; renamed ASTM International in 2001), and it doesn't certify products or host a list of compliant manufacturers, so adoption is evidenced by manufacturers' own declarations and retailer requirements rather than an ASTM registry.
The standard is known as ASTM F3340-18, developed by ASTM International in collaboration with leading outdoor companies (including Therm-a-Rest, Sea to Summit, Exped, NEMO, Big Agnes, and others).
Under this ASTM test, each mat is measured in the same way: the mat is placed between two plates, with a hot plate on top (heated to body temperature, ~35°C) and a cold plate on the bottom (~5°C). The testers measure the amount of energy required to maintain the top plate at body temperature.
The less energy needed, the more insulating the mat is, which yields its R-value. This controlled, repeatable lab test indicates that an
R-value of 4.0 from one company should provide similar insulation as an R-value of 4.0 from another company's mat, assuming both products
follow the standard. Labels on mats, as well as on manufacturers' or online shops' websites, generally state that the R-value complies with
this standard.
For campers and hikers, the ASTM standard basically means you can trust R-value numbers as a true apples-to-apples comparison of warmth. When you shop now, you don't have to guess whether one brand's 'R3' is different from another's - an R3 is an R3 (within small tolerances) across the board. Nearly all reputable brands now publish ASTM R-values for their mats.
The only area where I would exercise caution is on some of the sleeping mats from lesser-known brands that I have found on Amazon. I have tested a few of these as potential budget options, and their quoted R-values, in my mind, are sometimes questionable.
I've tried out some of these on consecutive nights along with my usual mats, when the temperature has been similar across those nights. A few times, the budget versions that didn't confirm that their R-value was tested in conjunction with ASTM F3340, kept me less warm than my normal sleeping pads from a brand that did confirm their R-value complied with ASTM F3340.
The vast majority of established companies and well-known brands have adopted it since 2020, which makes shopping much easier and more reliable. The introduction of the ASTM R-value standard was a big win for consumers - it levelled the playing field and removed a lot of guesswork.
At Walks4all, we welcomed this change because it helps adventurers pick the right gear with confidence, enabling them to stay safe throughout the seasons.
We have detailed buying considerations in our article on the Best Sleeping Mats. At Walks4all, I have learned through experience to trust personal comfort over general guidelines. If you often feel chilly at night, don't hesitate to invest in a warmer mattress or add a foam layer. It's better to carry a little extra insulation than to spend a sleepless night in your tent.
If you frequently camp, consider purchasing more than one sleeping mat. As I mentioned above, I have two main sleeping mats, one for summer and
a warmer one for the colder days in spring and autumn.
I often pair these with my lightweight closed-cell foam mat, which provides an additional R-value of 2 to complement my other mats. Being closed-cell foam, it is very hard to puncture or put a hole in, so it effectively protects my air mat. I used to use the old-fashioned closed-cell foam rolls that were frequently attached to backpacks, but I've now switched to an accordion-type mat - the Therm-a-Rest Z Lite Sol, which I can also use as a sit mat.
If you only want to invest in one mat, go for one with an R-Value that covers the coldest time you will use it. If you do use it in summer,
the mat simply slows down heat loss rather than providing warmth, so it will not make you any warmer than if you were on a low R-value one. My
reason for having the summer one is that it is very light and packs down a lot smaller than my warmer mat.
The other primary consideration is to ensure it fits within the footprint of your tent!
R-value recommendations aren't one-size-fits-all. Use the seasonal guidelines as a starting point, then adjust up or down based on your own tendencies. The beauty of the standardised R-value scale is that it gives everyone a common reference, but it's up to you to choose the number on that scale that suits your personal needs. When in doubt, opting for a higher R-value is usually a safe and comfortable choice.
Yes. A high R-value pad doesn't generate heat; it just slows heat loss, so it won't make you hot on warm nights. The trade-off is that the higher R-value mats generally come with extra weight/bulk rather than temperature.
Yes. When you layer pads, their R-values are additive (e.g., R2 + R3 ≈ R5). Pairing a thin closed-cell foam pad with an inflatable is a common strategy.
Aim for about R3 to R4+ for typical UK winter nights which range from 0°C to −5°C. Go higher (R5+) or layer pads if you expect snow or colder sub-zero temperatures.
Yes. Many closed-cell foam sit mats are around R1 to R2, enough to blunt the chill when you stop for a break. They're not for overnight use, but make a noticeable difference if you stop and sit on cold, damp ground or cold rocks.
No. Thickness affects comfort, but R-value depends more on materials and construction, such as foam density, reflective layers, and baffle design. Always check the stated R-value rather than judging by thickness alone.
No. R-value is a standalone measure of insulation, and there's no universal temperature conversion, although some brands share rough guides. Use the R-value to compare pads across makes.
Yes. A common rule of thumb is to add approximately +1 R-value compared to a warm sleeper under the same conditions. It's an easy way to build in a bit of a comfort margin. Many women also would benefit from a higher R-value.
No. Sleeping pads don't create heat; they reduce heat loss. So, a high R-value won't overheat you in the summer; instead, adjust your top insulation (such as a sleeping bag, etc.).
Layer another pad with it. R-values add, and even a thin closed-cell foam mat can boost warmth while protecting against punctures.
Ultralight backpacking pads top out around R 8.5 (e.g., the NEMO Tensor Extreme).
September 2025
