Abstract: A twin wall fiberglass tank and method of producing the same has an inner wall, an outer wall, and a core disposed between the inner and outer walls which forms a plurality of air gaps. Each of the inner and outer walls is formed of one or multiple layers of woven fiberglass roving and a mixture of resin and chopped fiberglass. The core includes a plurality of sinusoidal shape collated fiberglass flutes bonded to fiberglass scrim. The structure and configuration of the core allows it to be bent about an axis transverse to the collated flutes such as the curved surface formed by the inner wall of a twin wall tank. More particularly, after the inner wall of the twin wall tank has been formed, and prior to the outermost layer of the inner wall having cured, the core is wrapped about the inner wall in a barber pole fashion with the scrim forming the outermost surface. Immediately thereafter, the outer wall may be formed utilizing the scrim as a base.