I bought this shirt for a recent trip to Norway and Belgium.  I also wore it on a hike to Priekestolen which turned out to be very wet and rainy.  I attribute my relative comfort to this little shirt and it's wicking and warming abilities.  The XS fit tightly (as an underlayer should) and I'm 5' 0" and 130#.  I did find that even at my height the shirt rode up when I was hiking which made for some cold muffin top.  One other negative is that the neck is extremely tight when fully zipped.  I felt like my head was going to shoot off the top of my body, so I had to leave it unzipped.  Functionally, however, this shirt was great and the material did exactly like it should.