The armor of Stormtroopers consisted of 18 plastoid plates.
Plastoid refers to a specific type of substance utilized in the creation of armor.
Clone trooper armor incorporated form-fitting plastoid plates that were worn over a black body glove. This armor was susceptible to damage from the direct impact of blaster weaponry. Plastoid was also a material used in the construction of certain Separatist droids. Stormtrooper armor was constructed from a plastoid composite, rendering it resistant to chemical warfare. As a result, the helmets included an air filter along with an integrated oxygen tank.
The armor that was donned by the Dark Lord of the Sith known as Darth Vader made use of plastoid. Plastoid formed Vader's girdle. When Luke Skywalker burned Vader's armor on Endor, only the charred and warped remains of the partially melted helmet were all that remained.
Ap'lek, who was a member of the Knights of Ren, wore plastoid armor.