Pad to the Bone

Sleeping pad technology has come a long way since the closed-cell foam bedrolls you used in Cub Scouts. In addition to the ubiquitous blue pads of yore, we now have ultralight, super-compressible mats made of everything from palm-oil based foam to goose down to aluminized urethane film (yeah, crazy). Add to that the plethora of uber-plush inflatable camp beds available out there, and you have a product category about as diverse as Everest basecamp.

But your sleeping pad isn’t just there to cushion your weary body. When you lie down on your sleeping bag, regardless of fill type, the insulation underneath you compresses and is essentially useless in terms of warmth. This is where a sleeping pad comes in to save the day – sleeping pads are the insulation needed between you and the cold barren ground. (Big Agnes even went so far as removing the insulation from the bottom of their bags and replacing it with nothing but a pad sleeve.)

Different pads are designed for different temperatures and conditions, and it pays to pick one that’s optimally suited to the environment you’ll be sleeping in. Here are a few considerations to take into account when choosing between that six-ounce minimalist and the mega-fat camp bed.

R-Value
Aside from the visual differences in thickness, the main way to differentiate between the insulating abilities of a sleeping pad is by its R-value. You’ve heard the local gear clerk tossing around the term ‘R-value’ like it’ll cure cancer, but what exactly does it mean?

R-value is a measure of a material’s ability to impede heat flow, with a higher number indicating a higher capacity to stop heat from transferring. A pad designed for winter mountaineering will have a high R-value to stop the transfer of heat between your body and the ground. Whether a pad is made of closed-cell foam, synthetic insulation, or some kind of space-age, ultralight tin foil, the R-Value is computed in the same way.

According to Kerri Dellisanti, a media representative at Cacade Designs and Therm-a-Rest, R-value is computed using two different American Society for Testing and Materials (ASTM) standardized tests.

The first test uses a heated, constant temperature plate that delivers heat through a material whose other surface is bound by a constant temperature cooler plate surface. The R-value is determined by the temperature difference between the two plates and the power input to the heater.

The second test uses a heated, constant temperature plate that delivers heat through a material whose upper surface is exposed to constant temperature air. The R-value is then computed from the plate and air temperature difference and the power to the heater.

Due to the subjective nature of insulation (different people sleep warmer than others), there is no set R-Value scale that matches perfectly with temperature. According to Dellisanti, the minimum R-value for four-season use to the average person is somewhere in the neighborhood of 3.5 to 3.8, with three-season pads going down from there.

Materials & Construction
When it comes to materials, denser foams and fabrics lend themselves to higher R-values and better insulation, but they can also weigh you down on ultralight backcountry missions. Traditionally speaking, warmer pads mean bulkier construction. Thicker, more dense foam and heavier-weight shell fabrics stack up both the ounces and the overall size.

Some newer designs, however, such as the reflective barrier found on the Therm-a-Rest NeoAir, are extremely lightweight (14 oz.) and compressible but have a very high R-value because of its ability to reflect heat (imagine those shiny emergency blankets). Other models use compressible fills like goose down and polyester to insulate like a puffy jacket.

Conditions
Despite the proliferation of the inflatable sleeping pad in recent years, there are still a few reasons to hang onto that old foam roll-up sitting in your gear closet.

For alpine climbing and winter camping trips where sleeping on snow or wet ground is a definite possibility, a closed-cell foam pad paired with your inflatable mattress will both increase warmth and limit moisture absorption. This is especially important with mattresses that use down fill for insulation.

Camping in the desert, alpine talus, or thick pine forest where there are a plethora of sharp, pointy things threatening to ruin your cushy night of rest? A foam pad or an inflatable mattress with a reinforced bottom is the way to go.

Conversely, three-season inflatable pads usually pack up much smaller than any closed-cell models, which saves you valuable pack space, and are often more comfortable.

So for a comfy night’s rest, find the balance between warmth and light weight that best suits your camping conditions, and sheer exhaustion from a day playing outside will take care of the rest.