The mold-making material is dental alginate. It cures quickly and can easily withstand removal of even a fully erect penis without damage. I found the level of detail rather astounding...even the tiny veins and fine skin texture were reproduced faithfully. It deteriorates rather quickly too, so you need to make the dildo within a rather short amount of time after molding.
Incidentally, the alginate is available far more cheaply in craft stores that sell kits for molding hands and feet family keepsakes. I used this in my third (successful) attempt. Also resorted to shitcanning the container they provided, and simply filled a plastic pail with alginate and plunged my dick in.
