Dorsal Nylon Thruster Surfboard Fins Set - (Glass Filled FCS Base) Strong Glass Flex fins with Fiberglass reinforced Nylon construction by DORSAL. These performance tri-fins are based on the FCS G-5 fins design suited for middle to experienced level surfers. The two fin profiles used together create high drive for down the line speed and having the smaller back fin means they also offer great manoeuvrability.The combination of these tuned design elements with a strong durable nylon glass fibre composition ensures a great quality fin.