I wore it at a con, and it wasn't that warm. (about 2 or 3 hours waiting to get inside, standing in the sun.) but if one uses something that isn't 100% wool, then it will get hot.
Well, I think they use linen in their clothing, but as the tunic is supposed to be somewhat protecting (considering it is for a knight) it should be in a thicker fabric.I'm using linen otherwise for the cosplay.