I'm replacing all my cotton and synthetic shirts with wool and the hardest ones to replace are always the softest. Thankfully, these tanks are just as soft as worn in cotton, yet of a reasonably substantial material, doubled up where it matters on top. If you are the kind of person that is sometimes XS and sometimes S, especially if it is because you have bigger shoulders, I'd say size down. I have both and while both fit fine, the XS skims the body without excess fabric and also without being tight and the S is slightly roomier without being baggy. I prefer the fit of the XS and will eventually rebuy in that size.