[Written by IrnBruMan's wife]  I have several Modbod tops which I use to layer. Normally I wear a size large, but because these tops tend to be "form fitting" and I wanted to be able to wear this just as a top so I bought one size up.  It fits nicely.
As I mentioned I have several other tops by Modbod which I have had for quite a few years.  The fabric is not thin like so many tops, I hate it when my under clothing can be seen easily.  They hold up well if you wash them in cold water on delicate and hang them to dry.