As wetsuits continued to evolve, their use was explored in other sports such as open-water swimming and triathlons. Although double-backed neoprene is strong, the cloth surface is relatively rough and creates a large amount of drag in the water, slowing down the swimmer. A single-backed suit has a smoother exterior surface which causes less drag. With the advances of elastic Lycra backings and blindstitching, single-backed neoprene suits could be made that outperformed the early versions from the 1970s. Other developments in single-backed wetsuits include the suits designed for free-diving and spearfishing. Single lined neoprene is more flexible than double lined. To achieve flexibility and low bulk for a given warmth of suit, they are unlined inside, and the slightly porous raw surface of the neoprene adheres closely to the skin and reduces flushing of the suit. The lined outer surface may be printed with camouflage patterns for spearfishing and is more resistant to damage while in use.