Carbon fiber wheelsets ;are made of two components; carbon fiber and epoxy resin. When molding a carbon fiber wheel, pieces of pre-preg carbon fiber are laid into molds. Pre-preg is raw carbon fiber that is impregnated with an epoxy resin. Prior to the invention of pre-preg, raw carbon fiber was laid in place and epoxy resin was applied over the carbon fiber, which was a messy and difficult process. Pre-preg makes for a much cleaner and workable manufacturing process. http://www.haidelibikes.com/carbon-bicycle-stem/