Time of day could make a huge difference - if they did this close to sleeping, their body would be hot while winding down, and so would use less layers. If they

Time of day could make a huge difference - if they did this close to sleeping, their body would be hot while winding down, and so would use less layers. If they fell asleep with only a sheet compared to multi-layered thick covers, their temperature would be lower for the whole night. I know n=1, but when I started sleeping with only a sheet, my heart rate was at my lowest - my Apple Watch would ping multiple times a night because it was below 40. Can’t comment about being cold anymore because these days I sleep on top of a spiked mat which makes my back feel like it’s on fire for the whole night.