LOL. Okay, I don''t know if gases can pass through poly or nitro better, but everyone knows what is meant by "breathe" in this case. Wine does not inhale or exhale, yet we all know what is meant by "letting the wine breathe." So, a scientific test COULD determine if, for instance, a piece of wood put in a very dry environment would dry out faster with a nitro or poly finish. For Fender instruments, this is certainly a good point. Check this link out: http://www.caraguitars.com/fullerplast.htm This article mentions that moisture and gases might pass in or out of the wood through screw holes or paint fractures. Seems to me that control cavities and pickup routes would be the more obvious spot, but whatever.