The durability is not much of a concern, since there is only one, maybe two parts made off the mold. It would be great if the coating could be a consistent thickness. Variability in dimension can make big differences. The parts are used in the medical industry and are custom made for each...
The PU foam works really well as the mold, since it can be machined so easily. We often times mold other polymers which the foam works well on. If needed, we may have to switch to wood for the mold. It gets difficult because the molds are used once then disposed of and there are a couple...
I am working on a project that a mold is machined out of polyurethane foam. Polypropylene sheet is then vacuum molded over the polyurethane foam mold. Unfortunately, the polypropylene and polyurethane seem to bond slightly, as the surface of the PP becomes ruffed up like the PU Foam surface...