The Arc Reactor for the Iron Man Mark IV suit. One of two parts. Works with the Arc Reactor Light Diffuser Box also in my shapeways store:
https://www.shapeways.com/model/1811259/iron-man-mark-iv-vi-arc-reactor-lightbox-2-of-2-p.html?li=aeTabs. WARNING: Please take measurements before ordering to be sure this will work for your suit, your Arc Reactor chest cavity may not be the same size as others. Designed to print at a thickness of .72mm, (minimum for Strong Flexible Plastic is .7mm). This saves on printing costs and WILL need some reinforcement on your end. Most people use fiberglass resin.