Here are several methods I use to reinforce my 3d printed parts and some pros and cons to each. Each method is on a case-by-case basis and varies from project to project. Hopefully some of this is helpful! Some products/topics I forgot to cover are.... Flexible/High Impact urethane. Works similar to the casting urethane I show in the video but could be better for some situations. The EpoxAmite epoxy is nearly identical to Smooth-On's XTC3d coating but costs less by volume. I forgot to include Bondo body filler. It can work well to fill low spots before doing the laminating fiberglass and bonds well to polyester fiberglass resin. I don't use it often for this because it's slightly heavy compared to the cabosil (micro balloons) mixed with the resin. The micro balloons and chopped fiberglass strands can be used with both epoxy and polyester resins. I forgot to cover some of the urethane fillers. Probably not too important here but they are things I have used a few times in the past when using urethane to reinforce parts.