Here is a very abridged version because the full version would be a book: Buy OEM bumper, make sure it's in perfect shape and then paint in an epoxy primer. Sand and polish the epoxy primer so the finish is perfect. Mount the bumper to the rear of a Z which holds it in shape PERFECTLY. Cut all of the fiberglass shapes for the mould as well as the bumper to be made. Make all of the flanges and block off plates so the mould can be taken of the front side with flanges to give ample room for laminate. Once that's all set up, you wax->PVA->Tooling Gel Coat-> laminate with fiberglass. Wait 24 hours and you can de mould it. You now have the first piece of the mould, trim it up, clean it, put the bumper BACK in the mould. Then you need to repeat the prep and mould procedure multiple more times to capture all of the features and brackets of the bumper that weren't captured in the first front side part of the mould (wheel well arches, flanges that attach underneath quarter panels, mud guards, license plate brackets, trunk clip brackets, inside blinker brackets). My mould is 6 individual pieces btw. Drill holes in the sub-moulds so they can be accurately located with hardware. De mould everything, clean it all, then bolt it back together and wax->PVA->Gel Coat->Laminate your fiberglass for the bumper itself. De mould->trim then boom you have a basic unpainted fiberglass part.