Vinylester resins are stronger than polyester resins and cheaper than epoxy resins. Vinylester resins utilize a polyester resin type of cross-linking molecules in the bonding process. Vinylester is a hybrid form of polyester resin which has been toughened with epoxy molecules within the main moleculer structure. Vinyester resins offer better resistance to moisture absorption than polyester resins. Downside includes the use of liquid styrene to thin it out (hazardous to breath), sensitivity to atmospheric moisture and temperature. Requires specific window of atmospheric conditions to cure properly. Epoxy resin is preferable when bonding to dissimilar and already-cured materials. Vinylester resins bond very well to fiberglass, but offer a poor bond to kevlar and carbon fibers due to the nature of those two more exotic fibers. Due to the touchy nature of vinylester resin, careful surface preparation is necessary if reasonable adhesion is desired for any repair work.