It's easier to manipulate the PVC foamboard he is using here than regular PVC. Ive made sets of armor out of multiple materials (PVC pipe, sintra, aluminum, fiberglass, etc) and I'll say that this Sintra is one of the best to work with regarding Fett armor.
Its malliable when hot, easy to form, and is extremely rigid when cooled. Very pleasant material to work with when doing armor.