The Plasma Materials are the Xyz Monsters you use in order to Plasma Summon a Plasma Monster. Those monsters are sent to the Graveyard to Summon the Plasma Monster, with their Xyz Materials being placed in a place similar to where Xyz Monsters' Xyz Materials lay. Either the ex-Xyz Materials of the Plasma Materials or themselves do not play a significant role in the game, unlike Xyz Monsters and Composition Monsters, who use them to activate their effects.
● When LHK did the version 1.0 of the Plasma Monsters in his wiki, the ex-Xyz Materials that the Plasma Materials had are called "Plasmaterials". The idea got quickly removed.