Carbon fiber yellowing is a chemical reaction where the epoxy resin, the "glue" holding the carbon weave together, breaks down due to chronic UV exposure. Unlike paint, which has a thick clear coat, many aftermarket carbon components have thin or non-existent UV inhibitors.

Over time, sunlight causes the resin to oxidize, turning the clear finish into a murky, yellowish amber. This doesn't just look bad; if left untreated, the resin can become brittle and begin to delaminate or "cloud," leading to structural failure of the component's finish.