In the photos they appear to be a thicker material that is not transparent(standard t-shirt weight).  These are probably the thinnest material/fabric t-shirts I have ever seen.  No need for a wet t-shirt contest, these things are so thin they are nearly transparent.  You can easily put a newspaper/magazine under them and read with no problem.

For the cost, these should be made of better/thicker material.  I would NOT buy these again.