Okay I have a question as to what casting material would be best for my purpose. I am currently sculpting a helmet it is a complete original design that I am making. First I will say I am most familiar with smooth-on products and am primarily trying to work with their materials since I have used them in the past with great success. That being said coming to the casting I am trying to figure out the best product to use. Now what I am looking for is something that is fairly rigid and durable at a thin wall thickness maybe 1/8" - 3/16" thick I don't want to go any thicker than that or else it will be occupying too much room inside the helmet and I have designed it to hold a fan cooling system inside etc. What I have been looking at were the smooth cast ONYX but I have recently ruled that out as it may be a bit brittle at that thickness. My new options are epoxamite with some fiberglass layering an epoxy laminating resin, task 4 which has good strength in thin walled applications and is a plastic urethane resin, and also smooth cast 65D which is a semi rigid tooling plastic resin for impact resistance. The last catch is I would like to be able to use an RTV as a mounting base the fans kind of a vibration absorber. Possibly using some silpoxy adhesive to help with adhesion. I don't want to mount them with hardware mainly because I don't want hardware showing through at that part of the helmet. I hope my explanations make sense to someone. I am just a big fan of not wasting money when I can learn from others. Thanks in advance for any help you can offer me.