On March 14, 2026, in a stone barn outside Crickhowell in the Brecon Beacons, Astrid Pereira spread out three sleeping pads on a concrete floor and a wool blanket and slept on each for two nights in succession. The interior temperature, measured by a small data logger on the floor beside her, ranged between minus 1C and 2C across the six nights.
The pads were a Therm-a-Rest NeoAir XTherm NXT, stated R-value 7.3; a Sea to Summit Ether Light XT Extreme, stated R-value 6.2; and an Exped Ultra 7R, stated R-value 7.1.
The barn test was followed, in early April, by four nights in the Faulds bothy in the North Pennines, in temperatures between minus 4C and 1C. The same three pads. The same data logger. A different floor — old timber over stone, less thermally aggressive than the concrete.
R-value, as a measure, is a laboratory number. It is determined by ASTM F3340-18, which is a hot-plate test under controlled conditions, with the pad fully inflated, an idealized cold side, and no human body in the loop. It is a useful number. It is not the only number.
In the barn, on the concrete, the NeoAir XTherm was the warmest pad on three of the first four nights. Pereira recorded a back-skin-to-pad temperature differential of roughly 8C, comparable to what the lab number would predict. On the fifth night the temperature dropped to minus 1C and the Exped, slightly slower to lose heat, edged ahead.
The Sea to Summit Ether Light XT Extreme, at a stated R-value of 6.2, performed roughly as expected on the milder nights. On the colder nights it lost ground faster than the other two, which is consistent with the lower lab number. The pad was warm enough for Pereira to sleep without complaint at 0C with her usual three-season bag, but the margin was narrower than she had expected.
In the bothy, on the timber floor, the results changed. The Exped became the warmest pad on three of four nights. The NeoAir was a close second. The Sea to Summit, again, was the coldest.
Pereira suspects that the timber floor, which has a much higher R-value than concrete, narrowed the gap between pads. The pad that was retaining the most heat on its own was the one that benefited most. A reader who sleeps mostly in a tent on the ground will find different conditions again, with cold soil and contact moisture changing the result.
What this tells the prospective buyer is that R-value is a useful baseline but does not predict performance precisely on a given surface. Pads with similar lab numbers can differ by half an R-value in practice. Pads with very different lab numbers, on a warm floor, may differ by less than expected.
On comfort, the Sea to Summit is the most comfortable of the three by a wide margin. Its side rails support a side-sleeper better than the others. The NeoAir is the noisiest, with the well-known crinkle that the company has, over the years, only partially addressed. The Exped is the heaviest, at 690 grams in the long size, against 542 for the NeoAir and 700 for the Sea to Summit.
On durability, after thirty-eight nights in the field across the test period, all three pads remained leak-free. The NeoAir is the pad Pereira would worry about over a long season, having punctured two over the years on rough pitches, but the current sample held up well.
On packed size, the NeoAir wins easily. It packs to roughly the size of a one-litre Nalgene. The Exped is closer to a two-litre. The Sea to Summit is in between.
On inflation, all three use one-way valves and pump sacks of varying utility. The Exped's Schnozzel pump sack inflates the pad in three breaths. The NeoAir's stuff-sack-pump is acceptable. The Sea to Summit's Airstream Pumpsack is excellent in calm conditions and frustrating in wind.
A note on testing methodology. Pereira is one body weight in one age range with one sleeping bag. She is also a side sleeper. A heavier or thinner or back-sleeping reader will get different absolute numbers and possibly different rank orders. She has tried to control what she can.
For three-season backpacking down to 0C, all three pads are adequate. For winter use down to minus 10C with an appropriate bag, the Exped and the NeoAir are the right choices. The Sea to Summit is the wrong tool for winter use, despite its rated number being on the edge of acceptable.
For comfort on a long trip, where sleep matters more than weight, the Sea to Summit is the pad Pereira would carry. For weight-sensitive trips, the NeoAir. For trips where reliability and a slow leak in the cold would be a serious problem, the Exped, which uses a stiffer construction and has historically held up better in cold-temperature folding cycles.
Pereira has, in the end, kept the Exped and returned the others. She slept well on all three. She would not call any of them a bad pad. She would warn, as she has warned her navigation students for years, against treating a single laboratory number as a complete answer to a field question.
