Two sleeping bags can be 100% identical on paper and still feel totally different in the real world—and that’s what I set out to prove in this video. I went to Thermetrics in Seattle to see how temperature ratings are actually created, using a heated “thermomannequin” named Newton. The big eye-opener: sleeping bags are tested on top of a sleeping pad with an R-value of exactly 5. That means the rating you’re trusting is tied to a specific pad setup, not just the bag itself. From there, Zenbivy and I ran a field test with six strangers on a 20°F night. Everyone had identical sleep systems, but we swapped their pad insulation hour-by-hour by removing custom R1.1 foam layers, going from R5.5 all the way down to R1.1. Surprisingly, most people didn’t get nearly as miserable as they expected—even at the lowest R-value—and they could clearly feel the cold coming from underneath. To make sense of that, I did freezer testing at home and found something I’ve suspected for a while: inflatable pads don’t seem to perform like their advertised R-values in real cold, especially compared to closed cell foam. My takeaway is simple: if you’re using an inflatable pad for ~20°F conditions, I recommend aiming for R4 or higher. If you’re on closed cell foam, you can often get by with less—just don’t confuse “surviving” with actual comfort.