This manufacturing process converts reinforced fibers and liquid resin into a fiber-reinforced plastic using a pulling method, as opposed to a pushing method used in an extrusion process. The first step in the pultrusion process is to saturate the fibers by pulling them through a resin impregnator containing a bath made of epoxy, polyurethane, polyester, and/or vinyl ester. Often, fillers and additives such as colorant, fire inhibitors, and UV retardants are blended into the bath to enhance the finished product. http://www.topskyfrp.com/frp-pultruded-square-tube/