Vacuum forming is a simplified version of thermoforming, whereby a sheet of plastic is heated to a forming temperature, stretched onto a single-surface mold, and forced against the mold by a vacuum (suction of air). -- Vacuum forming (WP)I've just started looking into this topic; so far, it appears that:
Although it is a bit expensive (~$10/sq. ft.), it has some very nice characteristics. It can be cut and engraved by a CO2 laser. It is hard, durable, and handles temperatures up to ~200 C. However, like Acrylic, it tends to deform when heated.
If this could be done in vector mode, it would be much faster than raster engraving an image. It might also produce crisper results, if the touchable surface matches the mold more closely.