You need to mold it first out of clay, silicone, urethane, foam or whatever you choose, then use liquid synthetic rubber (which comes in an aerosol can & can be found at hardware stores).
Just use a mask, use slow, smooth strokes, apply a lot of coats for thickness, DO NOT DO IT IN COLD, BREEZY OR REALL HUMID WEATHER! And allow at least 24 hours to fully dry.
Just use a mask, use slow, smooth strokes, apply a lot of coats for thickness, DO NOT DO IT IN COLD, BREEZY OR REALL HUMID WEATHER! And allow at least 24 hours to fully dry.