Steel for the teeth, carbon for the spider, aluminum for the direct mount attachment. $149. I wonder if you could reduce the eventual cost of replacement by making just the wear portion of the chainring replaceable, and integrating the spider into the crankarm since the spider doesn't experience any wear.... no, that's too ludicrous to consider. (I'm sure it's a very nice chainring. Just funny how we end up engineering ourselves almost all the way back to older concepts.)