As expected, the phone has a polycarbonate (plastic) back. Jony Ive, Apple's senior vice president of design, described the iPhone 5C as "beautifully, unapologetically plastic. Multiple parts have been reduced to a single polycarbonate component whose service is continuous and seamless."
If you're wondering what makes a 5C different from the now-discontinued iPhone 5, it's basically this: new colors and feel, better front-facing FaceTime HD camera, and a slightly larger battery. Oh, and there's no 64GB version: you'll have to get an iPhone 5S for that.