Wings West poly-urethane parts are made by injecting the urethane material into a closed mold. Urethane is a flexible material that is similar to most of the original bumpers on current existing autos. It will not crack like fiberglass when it is stressed, however impacts or stress may damage the paint surface. Urethane is the best material to make aerodynamic parts out of since it is made in a molded process. This ensures that each part is consistent, so the fit is virtually guaranteed. Like fiberglass, urethane parts require prepping and priming before painting. Although the process used for urethane can be more labor intensive than fiberglass, urethane is still far superior in quality than fiberglass. Wings West parts have excellent fitment!