The plinth material is an important element of turntable construction. Both the material used, as well as the weight, density and finish of that material, can have a substantial effect on the sound. If the plinth does not offer sufficient dampening then microvibrations can make their way up into the stylus tip and into the bearing housing, having a negative effect on the sound.
Most Pro-Ject turntables use an MDF plinth for its extremely low resonant properties, but some also use an acrylic plinth as it has the same resonant frequency as vinyl and is equally effective at quelling physical interference.