I had to see it for myself, so I did the PUL experiment myself. Since I had some PUL from SoftBums from a project I was working on last summer-- I was all set!
I used boiling water and a small jar with a screw on lid. I added 150mL of boiling water to the jar, covered it in either the PUL or the outside of a disposable diaper. I took video at several different time points and pictures with better detail at the end of the video.
See for yourself!
Conclusion: The disposable diaper cover did not cause any condensation on the wine glass, thus we know no moisture was able to move through. On the other hand, the SoftBums PUL allowed condensation to form within the wine glass proving that it can breathe.
So relax, go fill up that wine glass. You're making a good diaper choice!