The SDX as a very special device implied special pad constructions.
ZI-pads: ZI stands for "zone intelligent". That means these pads could not only handle the velocity of the trigger event but also locate where the pad had been hit. This was achieved by using a semi conductor foil (FSR). The snare pad featured an additional mono trigger for the rim.
symbal pad: Similar to the ZI pad (it used the same FSR foil) but using a much more complex mechanical system to mount the pad. A torsion spring allowed the pad to rotate almost like a real cymbal when being hit.