So, I've realized the inch-an-a-quarter slabs I've had under my equipment (including my TT) to absorb vibration are actually something that HD sells as "Melamine" which isn't MFD like I thought it was. It seems to have a lower fiber density and is covered with some sort of Formica laminate.
I cut my pieces from an old school desk top (like a big metal-based teacher's desk).

Any idea if this stuff functions well as a vibration absorber, or should I replace it with real MDF?