The two cartoon Batman belts were made of long 5mm foam backers with 3mm and 5mm decorative design pieces glued on top. I glued nylon webbing onto the backs and added velcro for fastening. Both were hand painted with acrylic. Also, while gluing on the webbing, I held the belts in a bent position in order to have them retain some curvature after the glue dried.
Templates for both are available here.