Not heard that notion before. Sounds like one of Bradbury's ideas though, or something based on it. I can point out, on a related matter, that damping does not slow the speed of sound sufficiently to have an especially dramatic affect on the tuning frequency. And ideally, you don't want it to do anything at all to the fundamental in a properly designed resonant line. AFAIK, LHW's damping functions are, weight for weight, probably the best out there -perfect for an aperiodic line like Bailey's cabinets. But the material shouldn't be a particularly significant issue for QW lines, because they don't need a great deal to damp out the unwanted upper harmonics, which are pretty easy to take down.