Press releases

Don't be fooled by over-inflated R-values

26th July 2010

Multimat’s self-inflating and foam mats routinely feature among the vital pieces of kit taken by expeditions to the harshest environments on Earth.

From the Caudwell Xtreme Everest Expedition in 2007 to the Kaspersky Commonwealth Antarctic Expedition earlier this year, Multimat’s reputation has led international teams heading for the Earth’s frozen extremities to come knocking at their door before embarking on their frozen adventures.

However, there’s one recurring issue that confuses even some of the most seasoned explorers and that is the different ways of expressing a product’s thermal insulation used around the world.

On the face of it there are two different measurements - the Tog and the R-value or “Thermal Resistance value”. But what is often overlooked is that the R-value in the USA is significantly different from the R-value used by the rest of the world.

The R-value is usually expressed around the world in the SI Units – that’s “metric” to most people. It is the amount of heat that passes through one square metre of a material each second when the temperature on one side is one degree higher than on the other. Its units are “square-metre kelvins per watt” or m²·K/W – but not in the USA.  America still uses US Customary units, an imperial system similar to the British Imperial system, based on old fashioned square feet, Fahrenheit and British Thermal Units. So in America, R-values are expressed as ft²·°F·h/Btu. The result is two completely different figures.

It is particularly easy to confuse SI R-values and American R-values, because they are often cited without their units, e.g. R-2.8.

Adrian Stammers, managing director of Multimat, said: “It’s the poor consumer who suffers from this misleading situation – and not just ordinary campers but serious expeditions too. We make bespoke mats to order for some of the best known polar explorers and mountaineers in the business – some of them household names - but we still have to explain it to them.

“It also undermines Multimat and other UK-made products as many American mats have an R-value nearly six times what it would be if they were measured using the SI system that we and the rest of the world use.

“We’ve already put the record straight on our website and in our product brochure. Now we’re broadening our horizons and embarking upon an educational campaign to try and explain it to the camping community at large whenever we can.”

There are conversions that can be done to enable campers to compare one product with another, though you will need a calculator; a US R-value is 5.7 times the UK R-value, so divide the US R-value by 5.7 and you get the equivalent UK R-value.

“This still requires campers to know that the mat they are looking at is quoting American R-values,” said Adrian Stammers.

“I tell people that if the R-value quoted looks suspiciously high in comparison with other similar products, especially if it is an American brand, treat with caution. Of course, American manufacturers love R-values because it makes them look more thermally efficient than British mats when, more often than not, the opposite is true.

“At Multimat we usually quote tog values to avoid misleading comparisons. Tog (from the Latin word toga) was developed for the British textile industry in the 1960s as an easier system to use for textiles’ thermal insulation qualities. 1 tog is 0.1 RSI  or 10x the R-value when expressed in SI units.

“As a rule of thumb, our Trekker 75 self-inflating mat in our All Seasons range has a tog value of 10.0. That is equivalent to an R-value of 1.0 using UK (SI) R-values and is pretty much as warm a mat as you can get. If a camper is quoted a figure significantly higher than that for a mat they should check with the manufacturer.”

Contact Details

Beacons Products Ltd.
Unit 10, EFI Industrial Estate
Brecon Road
Merthyr Tydfil CF47 8RB
South Wales UK
+44 (0) 1685 350011


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