A guy at the REI garage sale told me my sleeping pad rating was a lie, so I tested it at 8,000 feet
I used to brag about my pad's 15 degree rating like it meant anything, lol. A guy in line at the Denver REI garage sale asked where I camp and when I said Guanella Pass in October he just laughed and said "that number is for a warm body on a hard floor, not you on snow." So I slept out at 8,000 feet twice, once on bare ground and once with a $12 closed cell foam pad under it, and the foam night was warmer by a lot. Now I pack the cheap foam pad every cold trip and I stopped trusting the temp rating on the box. Anyone else find that stacking two cheap pads beats one fancy one?
So you changed two things at once and now you're sure the foam pad was the reason? Bare ground pulls heat out of you way faster than snow or a tent floor, so of course the second night felt warmer, you were on a totally different surface. And $12 foam pads come in different thicknesses and densities, some are basically packing material. Did you run the same pad on the same ground on back to back nights, or just compare two random trips?