I knew it was simple.....
Plastic cores, just like I thought...
From Classic's web site....
Each dash pad is wrapped in vinyl and manufactured on an ABS frame to reinforce the weak spots of the original dash. These dash pads feature correctly located mounting studs for a proper fit and are available for cars with or without air conditioning,1 or 3 speaker holes, and in all factory colors. Please specify color when ordering Made in USA.