Sleeping mat R-value explained

Our guide to sleeping mat R-values. Find out what they are, how they’re tested and the recommended numbers for seasonal camping.

Rab Ionosphere and Stratosphere Packaging

You’ve read our guide on how to choose a sleeping mat, you’ve decided whether inflatable or closed-cell is best for you, the shape you’d like and whether you want to match the colour of your sleeping mat to your thermal leggings, but the most important thing is warmth. It’s time to get into the nitty-gritty of R-values. 

Your sleeping mat’s R-value is a measure of thermal resistance. It’s how much it insulates you from the ground. As someone who once went on a mountain trek and punctured my inflatable sleeping mat a week before the end, I can vouch for how important it is to have an adequately insulated sleeping mat. My bones aged at least 30 years each night.

So why doesn’t everyone just go for the highest R-value out there and sleep in their tents elevated so far off the ground that they feel like the princess from The Princess and the Pea? It’s probably no surprise, but sleeping mats with higher R-values are often bulkier and heavier, and they also tend to cost quite a bit more. Plus, camping out at Glastonbury is a different kettle of fish to camping on a glacier. 

Don’t be afraid to head to your local Decathlon/Cotswolds Outdoor/Millets and test a few out. This is effectively the mattress store trip for backpackers, and how often do you get to lie down and have a nap in a shop?

Editor’s notes

In an ideal world, the kit cupboard of every adventurer would have 3-4 different sleeping mats for the changing weather conditions and seasons.

Unfortunately, it’s just not a reality for the majority of us – if you’re looking for a one-mat-fits-all approach, it’s best to go with a 3-season mat with an R-value between around 2 and 4 (5 if you’re a cold sleeper).

What are sleeping mat R-values? 

The R-value of a sleeping mat is its resistance to heat flow. This insulation can be measured in half points. R0.5 provides the least insulation – a sleeping mat with this R-value will give you little more insulation than sleeping directly on the ground. 

The scale goes all the way up to R6+, which covers heavy-duty sleeping mats built for seriously extreme conditions. Note: If you’re planning an expedition to the North Pole, don’t use an inflatable sleeping mat, they don’t work well in such extreme conditions and risk puncturing. If that’s the kind of adventure you’re heading out on, get gear advice from a specialist.

How are R-values calculated? 

Brands all have to undergo the same checks to calculate the R-value of their sleeping mats. This means that, unlike high street clothing stores, you won’t find any wildly fluctuating measurements here. Instead, you can accurately compare sleeping mats from different brands knowing that they’ve all had to jump through the same hoops. 

The standard ASTM F3340-18 test is carried out by holding a camping mattress compressed between a guarded hot plate and a cold plate (if you’re a details person, the full test specs are here).

Recommended seasonal R-values 

Here’s our guide to seasonal R-values, helping you to choose the best sleeping mat for your next trip.

Summer (R1 – R2)

If you’re an occasional summer camper who’s planning a mid-summer festival itinerary, you might be able to get away with a really low R-value mat of between 1 and 2. If, like me, you’re a cold sleeper, I’d recommend going for an R-value of 2 even for these summer campouts. 

Spring/Autumn (R2 – R4)

Many of us fall into the bracket of camping out when it’s a little chilly, but splashing out on the warmth of a B&B or bunkhouse when the frost sets in. A sleeping mat with an R-value of between 2 and 4 is adequate for most of these (UK-based) adventures. 

Winter (R4 – R6)

When cold weather doesn’t stop play, you’ll need a well-insulated sleeping mat. For camping in the cold, with a possibility of ground frost, look for a mat with an R-value of between 4 and 6. 

Extreme cold (R6+)

If you’re hardy and still sleeping under canvas even when temperatures are below freezing and the ground is frozen too, get a sleeping mat with an R-value as high as you possibly can. In these cases, there’s no such thing as too much insulation. An R-value of 6+ is a must. Don’t forget a really well-insulated sleeping bag to complement – check out our guide to the very best

Stacking sleeping mats for combined R-value 

Here’s a nice little hack: sleeping mats can indeed be stacked to increase their R-value. It’s incremental, so if you own a summer and a spring mat with R-values of 2 and 3, you could layer them on top of each other to have an R-value of 5, without having to dash out and buy an expensive new sleeping mat. 

Put the warmest sleeping mat closest to your body for the best insulation (e.g. in the above example, the sleeping mat with the R-value of 2 would go on the ground, with the R-value 3 stacked on top of it).

Which sleeping mat has the best R-value? 

Great brands that sell high R-value sleeping mats include Therma-a-Rest, Sea-to-Summit and Exped. Each of these stocks sleeping mats with R-values of 5+.

Thermarest NeoAir Xtherm NXT

Recommended Product Therm-a-rest NeoAir XTherm 

The Therma-rest NeoAir XTherm provides the best warmth-to-weight ratio of any sleeping pad ever made. An R-value of a whopping 7.3 and a weight of just 439g makes the mat the perfect candidate for lightweight, extremely cold camping. 

FAQ: Sleeping mat R-value explained

Have a question about sleeping mat R-values that you’re hoping to answer?Check out the most popular questions about the sleep system foundations below.

Generally, yes, higher R-value sleeping mats will be more expensive – but you’re paying for quality.

If you usually backpack in summer, you can get away with stacking your sleeping mats or using a sleeping mat with a lower R-value, but if you’re a habitual winter adventurer, we’d recommend investing in something more insulating.

An R-value between 2 and 4 is good for most UK adventures, but take a look at our guide above for further assistance.

A fantastic sleeping mat for UK backpacking is the Rab Ionosphere 5, which has a tiny packsize of 23cm x 11cm and weighs just 550 grams. This mat has an R-value of 4.8 and an inflated thickness of 8cm.

Answer this question by asking yourself where and when you’re going to be using your sleeping mat. Is your priority weight or warmth? If you’re going van camping, you can take something much heavier than if you’re hitting the trail with a backpack.

Still not quite managed to answer your question? Don’t be afraid to reach out to the Adventure Pending team over on our socials – we’ll try our best to get to the bottom of any issues or concerns!

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