There are several types of glass cloth you’ll see at body repair shops, plus resins with and without epoxies. These are matt mold, standard woven cloth, chopped glass, SMC, and polyester resins. Glass cloth comes in varying grades (thicknesses).
Matt mold is often used for body work because of its random pattern. It won’t leave a noticeable ‘weave’ in your paint finish. Woven cloth is primarily used for building up structure or splicing sections of products made of the same material.
Although woven cloth has better strength and crack resistance, matt mold gives auto body technicians an advantage of being able to work areas without the fear of sanding down to the visible weave of the woven cloth.
Ideally, a fiberglass car repair is made by using woven cloth and then using matt mold to cover the repair area. Bodywork always requires that the repair be blended into the surrounding area.
A deep depression must to be sanded wherever the woven cloth is to be used. Because of this, automotive body workers use matt mold for much fiberglass repair work. They get the strength they need by using an adequate thickness.