As I've mentioned before, my body is usually quite warm.  I sweat a ton on ascents, so layering is 100% necessary. It's great to be able to peal off my jacket after a short warm up and not have to worry about getting too cold.   I now have the perfect T-shirt for this spring warmth.    The Lundhags Fulu Merino climbing T-shirt is awesome.  It's as soft as any t-shirt I have ever worn, but it's also amazingly light and wicks moisture from your skin very effectivly.  After reaching our first peak, I went jacketless for only a few minutes and the shirt was dry like I hadn't even left the car.