So, basically you pour the neoprene that's already mixed into the mold, let it settle for a few hours while water evaporates out of the mixture, and then you can top it off. You can also make hollow-skin like casts with the neoprene if you cast in plaster... I have no idea if this will work in the 3D printed mold without a mold release, but it specifically said on the website not to use mold release, so I'm giving it a shot! This weekend, I think I'll try and pour some neoprene into a plaster mold and see how that goes.