Fiberglass is stiff and tough for heavy conditions or surfers that appreciate very stiff fins.
Flat foiled fins break free sooner, and are better at controlling speed. Often surfers prefer them in fast powerful surf where they do not need to create additional speed. If you have muscle memory from riding glass-ons, flat foiled fins will feel the closest.
Thank you for surfing Longboardhouse.com. Call 1.800.844.6211, or e-mail, Longboardh@aol.com.