I don't understand what's happening here, none of the mods I am using are interfering with cold sweat.

Make sure your configs are set correctly. Does the leather helmet have a tooltip showing that it gives insulation?

I have no idea how I fixed it, but it seems to work now, the leather helmet, and the other armours with built-in insulation, were showing on the tooltip, however now it seems as though it must have been the wrong tooltip, as I remember it, it was showing +20 something on the leather insulation. Any way, I solved it somehow.