Poly vinyl alcohol. It's a spray on mold release (spray with paint sprayer). You build up several layers to form a film that is almost like saran wrap and can be peeled off when cured or washed away - it's very water soluble and easy to remove. It makes a pretty bullet-proof mold release or an air barrier for gelcoat that you need to cure in the open air.

When spraying on a waxed surface, you have to mist on the first coat or two and let each coat dry for about 15 minutes. Then you can lay down two or three nice glossy coats. It dries pretty smooth and glossy but it's about impossible to get a completely glassy smooth finish on it so it's probably not the best thing out there to use as a release for a very high end mold. It is waterbased so it works very well with ester based resins. You have to be sure to get a thick enough barrier when using epoxy...but it doesn't seem to affect the finish of the epoxy at all.

I buy mine at www.uscomposites.com but I'm sure www.fiberglasssupply.com or www.aircraftspruce.com has it as well.