I modeled the pumpkin in Blender, then cut out the profile in 1″ wide sections of standard insulating foam using the makerspace’s CNC router. The pieces were then hand-finished and a couple of coats of Durham’s Rock Hard Water Putty were applied to strengthen it and seal the foam (because foam melts in a really cool way when you apply spray-paint to it).
Jason H., the maker who approached me with the project, helped in the finishing, painting, and decorating aspects.