Can’t speak for what they claim, but have not seen comparative evidence that indicates non-filled perform a a higher level than filled. Important to understand that the deflection that is talked about on irons is very small and as the loft increases, any effect is reduced. The polymers, at least the ones we are familiar with, are not rigid and do not inhibit any face deflection that occurs. Having done many hollow iron designs, one of the challenges that can occur is the sound. Only speaking for our own design, and others we have tested with polymer, we believe the sound aspect is greatly improved when the cavity is filled on these types of iron designs. We have hit and tested the Pings and found them to perform well, no better and no worse, than other hollow designs with regards to ball speeds, spin, etc. Of course it is difficult to get an apples to apples comparison because of variations in lofts, but generally speaking, they performed as expected. Feedback we have received is that the sound is “different” on the Pings. You would have to hit them to make your own judgement. I prefer the sound of our TS-1 and TS-2, but obviously that is a biased opinion.