Choosing a Sleeping Pad: R-Value, Foam vs Air, and What Actually Matters
The sleeping pad is one of the most important items in a camping kit and one of the most frequently underbought. Its function is insulation between the sleeper and the ground — a sleeping bag rated to minus 10 degrees C provides almost no warmth when compressed against cold ground because down and synthetic insulation both lose insulation value under compression. The pad provides the insulation that the bag cannot. Understanding the R-value standard is the starting point for any pad selection.
The R-value standard
R-value measures thermal resistance — the higher the number, the more the pad resists heat transfer to the ground. The ASTM F3340-18 standard (adopted in 2020) provides a standardised testing methodology that allows direct comparison between pads from different manufacturers. Before this standard, R-values were self-certified and comparison between brands was unreliable.
The guide to R-value by temperature:
R-value 1 to 2: summer camping on warm ground. Temperatures consistently above 10 degrees C.
R-value 2 to 4: three-season camping. Adequate for most spring, summer, and autumn conditions in temperate climates.
R-value 4 to 6: cold-weather and early winter camping. Shoulder season in alpine terrain; shoulder season in sub-arctic climates.
R-value 6 and above: genuine winter camping on snow or frozen ground. Multiple pads can be stacked — the R-values add arithmetically.
Closed-cell foam
Closed-cell foam pads — the Therm-a-Rest Z Lite Sol and the Ridge Rest are the benchmarks — have no moving parts, cannot puncture, and are impervious to moisture. They are also bulky (they strap to the outside of a backpack because they cannot be compressed) and have the lowest R-value per centimetre of thickness of any pad type. A Z Lite Sol is 51 mm thick and provides an R-value of 2.0 at 415 grams — adequate for three-season camping and extremely durable.
The practical use case for closed-cell foam is: as the primary pad for summer backpacking where weight and packability are the priority and ground temperatures are reliably warm; as the bottom pad in a winter two-pad stack (closed-cell below, inflatable above); and as a durable sit pad and emergency bivy ground insulation.
Inflatable sleeping pads
Inflatable pads (Therm-a-Rest NeoAir, Sea to Summit Ether Light XT, Nemo Tensor) pack smaller and provide higher R-values for the same weight than foam. The NeoAir XTherm at R-value 7.3, 430 grams, and a 7 x 24 cm packed size is the performance benchmark for winter ultralight use. The trade-offs are: puncture risk (a small puncture deflates the pad over hours, requiring a repair kit and the ability to find and patch the leak in the field); and the crinkle noise that some inflatable pads produce when the occupant moves (less common in current-generation designs with polyurethane laminate rather than foil thermal barriers).
Insulated vs non-insulated inflatables
Non-insulated inflatables (the original NeoAir, basic camping inflatables) have an air column interior that allows convection — warm and cool air circulating inside the pad, conducting heat away from the sleeper. Insulated pads add either a reflective thermal barrier (NeoAir's Triangular Core Matrix) or a down or synthetic fill inside the air chambers to break up convection. The R-value difference between an insulated and a non-insulated inflatable of the same thickness is typically 1.5 to 2 R-values.
Self-inflating pads
Self-inflating pads combine a foam core with an airtight outer shell — when the valve is opened, the foam expands and draws air in. The Therm-a-Rest ProLite and Trail Scout are the standard references. Self-inflating pads provide a comfortable sleeping surface, moderate R-values (typically 2.5 to 4.5), and no puncture risk in the foam core. The valve and shell can leak if the valve seat is damaged. They compress to a smaller packed size than closed-cell foam but larger than a comparably rated inflatable.
Width and length
Standard pad width is 51 cm; wide pads are 64 cm. The difference matters for side sleepers who roll off a 51-cm pad. A 183-cm length is standard; a 168-cm mummy-cut size saves 100 to 150 grams but requires keeping shoulders and feet on the pad to avoid cold spots. Most people who select the shorter length regret it. For winter camping, foot insulation is critical — a short pad that leaves feet on the ground surface causes cold feet regardless of sleeping bag rating.
Pad combinations for winter
The reliable winter approach: a foam Z Lite Sol (R-value 2.0) as the bottom layer, with a NeoAir XTherm (R-value 7.3) on top, giving a combined R-value of 9.3. The foam pad prevents ground contact damage to the inflatable valve and provides backup insulation if the inflatable deflates. Total weight: 415 g + 430 g = 845 g, which is acceptable for winter camping where overall pack weight is inevitably higher.