I have a long term problem of being a size "medium-large" which makes it difficult to find shirts that fit well. I ordered the medium Intelliskin, but it is too tight. It does do what it says with regards to posture and I found it especially helpful when sitting at my work desk. This is where my posture tends to degrade the most. But it was too tight to wear for very long.

I have ordered a large and will try it later today. Hopefully it fits right and is not too big to cancel out the benefits.