I found the Dampp-Chaser's patent online: <a href="http://www.freepatentsonline.com/6133519.pdf" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">http://www.freepatentsonline.com/6133519.pdf</a> (you might have to create an account to look at the pdf, for some darned reason) According to the abstract, the under/back cover patent is for a "...moisture impervious aperture free sheet...".  In the detail of the patent write-up, under "Background of the Invention" it specifies "MYLAR or felt" (caps theirs) "... having a plurality of apertures or holes..." (which, to my mind, contradicts the abstract portion... but then again I'm not a lawyer.) So, what sort of fabric/material is Dampp-Chaser's under/back cover made of?  I'm not a rocket scientist, nor even a acoustic engineer, heck, I'm not even an RPT, but the idea of Mylar back/under cover on a piano sounds to me like it would sound a bit bizarre. Wouldn't it?? And wouldn't felt mute and muffle the sound?  (see previous disclaimers regarding my qualifications) I wonder what a "plurality of apertures or holes" means... several holes and/or apertures in the cover, or is that phrase intended to include an open weave like speaker cloth, being what it sounds like many techs are using.  An open weave certainly has a "plurality of holes," but it would make a lot more better sense to say "open weave fabric." Please understand that I'm not trying to get around anyone's patent, or infringe on same... when the time comes I'll order the DC cover simply for the convenience of it, if for no other reason. My curiosity is piqued about this patent for a new way to use a piece of cloth... and I'd just like to understand it better. Judging from the amount of traffic generated by this topic, I don't think I'm alone. Paul Bruesch Computer Geek and PTG Associate, who typically plays by the rules but wants to understand them. And I don't run with scissors.