Are you sure it's PVC foam? It's probably EVA foam if it's sold in mats. PVC foam is also good for costumes, but it's more of a rigid plastic than EVA foam, however both are forgiving and easy to work with. The Mandalorian Mercs like to use PVC because of the relatively little flex and hard, smooth surface, along with it's low malleability temperature. Their application is well suited as they have small plates with only slight curvature.
Building a Masterchief costume out of PVC foam would be quite a feat, and not an easy one. Building one out of EVA foam can be done in a month.