They are a poly overlay here is a paragraph of their description
SuperMax poly pulleys have been on the market since the early 70's and as many of you know, they do not wear out! We offer these new overlays in black and a rainbow of popular colors. They run very quiet, so the "Squeal" and "chirping" noises emittted by metal pulleys is gone. These poly pulleys are not affected by sand or small debris. These pulleys should outlast the motorcycle, as long as the recommended tension and alignment are maintained. Many customers ask, "How far will your pulleys go?", and our answer is ... "We still don't really know!".
One of our club members contacted 'SuperMax' and was quoted $470 to repair a rear pulley plus $60-70 return shipping. As a new pulley from H-D is about £120 ($175) in the UK and lasts about 40k miles (5 years riding for the average biker over here) I don't think this is worth pursuing, thanks anyway.