Best thing about these is the extreme light weight and flexibility - paddling feels like you're wearing just a rash top. OK not super warm - not as warm as 1.5 or 2 mm tops. But just enough reflective heat on the inside (because of the inside reflective skin) to keep warm in 20+ degree water and a bit of wind. I intend to try it underneath a 2 mm wettie through Autumn as the water gets colder. Comfort ++.