Resins are typically lower molecular weight polymers produced by the polymerization of monomers containing areas of unsaturation. There are several classes of resins, of which non-reactive resins are the most popular. These hydrocarbon resins (C5, C9, DCPD, mix, etc.) and phenolic resin (novolacs and resoles) can be used as tackifiers, performance adjuster, glass transition temperature modifiers, and even homogenizing agents. Some of the largest market users of resins include the adhesive customers (hot melts, pressure sensitive adhesives), but the demand into many rubber formulations is increasing.