Good question. When I've used cap shirts they've been warm and comfortable while not moving much. But while moving I've been a bit warm in them. I could have gone down to a cap2 and considered that. But others using merino (Icebreaker) in particular have touted the quality highly. They've said it layers better, wics moisture well, etc.
Maybe there are arguments for and against each material. For me, I'm going off of several people that like the Icebreaker products.
