I currently have floating around my head. I have 2 FDM printers and a Resin Printer.  So for the inside I was thinking some sort of 3D Printed insert made out of TPE. The outside is where it gets hard. Now I think carbon fibre is my best bet but I don't know if I can get the amount I need with my budget, so pvc is another thought I had. Whatever it is it can't shatter.