This plastic card is not the thin plastic card used by modellers and written about by scratch-builders, but a thicker and softer plastic card used by sign makers and for use in stores as POS. If in doubt, you should be able to easily flex the card and mark the surface with your fingernail.
The card can be cut easily and textured by pressing stones or sandpaper into the surface and sanding or texturing with a wire brush. It can also be glued together with superglue and if layered can produce very strong structures.
I find that you can pick up off-cuts very cheaply and sometimes for free, if you contact department stores who are usually only too pleased to supply the out-of-date advertising material free of charge.
My latest batch is a Stanley Knife advertising board. Be aware that the same plastic card is sometimes covered with coloured sticky-back plastic, which can be easily removed.