The mold is high density foam on 1/2 inch plywood base, the whole thing is coated with quality acrylic gesso paint. The surface is completely sealed and can easily be drawn on with a felt pen.
The mold surface can be easily pinned to hold pieces before soldering.
The surface repels flux, it runs off and does not absorb into the mold.
Solder directly on the mold, it won't hurt it.
This mold can be reused endlessly.