Our company started with a core need shared by all mountaineers and backpackers: a better night at camp. Back in the day, the biggest obstacle was creating comfort on the cold hard ground where we make camp. Throughout the night, the cold ground can rob your body of heat, which means waking up tired and robbed of the essential energy to tackle the next day’s objective. Sure, you want something thick and plush, but perhaps the most important function of your sleeping pad is its ability to resist the cold. This is what makes sleeping pads so crucial to resting better. We measure this function with R-value.
R-value and how we test it
Technically, R-value is a measure of thermal resistance; the higher the R-value, the more thermally resistant the material or structure is. This isn’t just used to measure sleeping pads. It’s used by engineers and scientists to measure everything from windows to fiberglass. Our team believes that it’s also the best way to measure the insulation of our pads.
We measure every mattress design in our on-site cold chamber, kept at a cool 4C (39F). Inside this thermally-sealed container, a mattress is placed between two metal plates. A section of the bottom plate has been turned into a large sensor and is kept at a steady temperature with a measured electrical current. A mattress that provides a lot of insulation will help keep the bottom plate warm and, as a result, the sensor will require less electricity (energy) to maintain its temperature. A mattress with less insulation will require more energy. This measurement–the amount of energy required to maintain the plate’s temperature– plugs into an equation to provide an R-value for each mattress–the less energy required to keep the plate warm, the higher the R-value and vice versa.
Some companies test their mattresses while others “estimate” their ratings. It’s important to keep that in mind when comparing R-values from different companies.
R-value At Camp
If you were to make camp for the night, rolling out your sleeping bag and laying directly on the ground, you would quickly get cold due to convective heat loss between your warm body and the cold ground. The compressed down would fail to create an insulative layer between the two. By selecting an appropriately insulated sleeping pad, you save your body precious calories and stay warm throughout the night, waking up energized and ready to take the trail. This process is what makes a sleeping pad so important.
How To Use R-value
R-value can be very informative while building your sleep system for a specific adventure. Let’s say you’re going into the High Sierra in September. You’ll be expecting brisk nights, but there’s real potential for frigid ones too. Do you bring the giant 0F winter sleeping bag to be safe or your three-season bag and risk a few cold nights? Most people will make a decision based on bag warmth alone, but by factoring in mattress warmth, you suddenly have more options for making your sleeping bag perform better on the margins of its comfort rating. For instance, on a NeoAir® XLite® (R-value:3.8, Weight: 12 oz.), you should get the comfort your bag is rated for. However, jump up to NeoAir® XTherm™; (R-value: 5.7, Weight: 15 oz.) and you could get by on those coldest nights with a greater comfort margin for only an extra 3 ounces – a lot better than jumping to a winter bag that could add up to a pound of extra weight.
While there are many variables that affect your sleep system’s warmth, this is a crucial piece to a very complicated puzzle. That’s what intentional gear selection is all about. Collectively, fine-tuning everything in your pack, and making sure you sleep well every night, will make a big difference in the way you feel on your next adventure.
If you are interested in learning about the new standard for sleeping bags taking effect in 2020, check out “The ASTM R-value Standard: Rating Sleeping Pad Insulation”.
If you want to find out more about how R-value compares to pads that receive temperature ratings, check out “How Warm Is A Sleeping Pad: R-value vs. Degree Ratings“.