Gold Bond® brand eXP® Interior Extreme® Gypsum Panels consist of a moisture- and mold-resistant gypsum core encased in a coated, specially designed fiberglass mat on the face, back and sides. It is available in either a Regular, Type X or Type C core (often specified where the weight and number of gypsum board layers are a concern). The glass mat is folded around the long edges to reinforce and protect the core.