This shirt does not seem to conform to any size standards of other shirts Ive ever purchased.  I normally wear a medium or large in a petite if I can find it or a normal if I cant.  This shirt is constructed with raglan sleeves with the armhole opening very tight.  You can see this pulling even on the pictured models.  I tried both the medium and the large sizes and the tight armhole was a problem on both.  While the body on both was roomy enough the armhole was not and I do not have large upper arms.  On the large the sleeves were about 7 inches too long and the body length was past my thighs.  I could have worn it as a tunic!  Even in the medium the sleeve and body length were much longer a than other shirts in the same sizes.

Having said that, the shirts were well constructed of a soft drapy fabric.  Even though the literature claims they have some kind of odor defense technology I suspect thats a tip off that they are not breathable.  I didn't test that because the shirts are going back because of the very strange fit.