Abstract: Mold halves are formed from thin, flexibly stiff, rigid polyvinyl chloride film having a thickness of 0.010 .+-. 0.003 inch and which is deformed to conform to opposite surface contours of a structure to be produced. The mold halves mate along a parting line to define a mold chamber in the shape of the desired structure and are formed with an access opening to the chamber, marginal regions coextensive about the chamber from the parting line, and conjugate protuberances on the marginal regions. The film is thin and pliable enough for pins to be inserted cross-wise through the protuberances to secure together the mold halves, yet thick and rigid enough to support casting material poured therein and flexible enough to be peeled from the partially set product.