As you would expect these shirts fit tightly, but they are supposed to.
I wear them most days to work to help regulate my body temperature (my body tends to heat up too much resulting in sweaty situations), and they are honestly brilliant. My confidence is now much better, with the knowledge that I'm not going to end up with unsightly patches.
If you sweat at work, pits and/or back, you will not regret trying these. Previously I've tried other types of vest, or more preventative measures such as Dri-Clor (which is an excellent product, but faffy to maintain it), but these shirts are the best.