I used the vacuum former to heat and form sheets of plastic (from Tap Plastics you can get sheets of Polypropeline) to make molds. I like working with nature so I used pieces of wood, bark and pine cones cut in half lengthwise. I had to cut the pinecones or else the plastic would wrap around them and I wouldn't be able to get them out. No undercuts. I also got one pre-formed mold sheet to accomodate many small resin pieces to be made.