Only Ultraguard has a special formula that has flexural enhancers in the product. Fiberglass walls and one piece fiberglass pools will flex 12 months a year. The UltraGuard 6000 or 3000 with flexural enhancers will meet the specification standards of expansion co-efficient. All paints, epoxy etc., become brittle in a short amount of time which could cause unsightly stress cracks on the walls. Only UltraGuard will move with the movement of your fiberglass pool and will not have stress cracks.