-40� doesn't even compute for a guy from the South. Down in the teens is about the best we can pull off with the occasional single digit and rare minus single digit. Chill factors with humidity, on the other hand...
Fact is, much below low 20�'s and I have little interest in being out anyway, at least not sleeping out.
Ditto on little interest in sleeping out in such cold. Avoid it when I can. I cut short a whitetail rattling trip in late Nov. due to guesstimated somewhere below -10F and my hands cracking painfully in the cold. My grandson demoed that the rib cage on a skinned frozen whitetail rings like a dull bell when whacked with metal.
Somewhere around -30 and lower it feels more like pain than cold to me. In -40 and lower many materials change their properties, some getting brittle, some stronger, oil lubrication properties change I'm told. The old ensolite foam pads shatter with a pattern like a rock hitting a windshield. On one of the trips I rated at -40 my 15 year old son had frozen patches on his nose and cheek in the time it took to walk 50 feet from a heated vehicle. Time to go home.
