Star Systems Twin Apex Custom Mens Rigidity: Thicker boards (like our Size:Stand Up Paddle Board 11'6 Rigidity: Thicker boards (like our 5" foam core) provide greater rigidity and weight capacity Our game changing approach starts with quality materials like limestone based neoprene and specially developed insulation with stretch zones in high movement areas—what we call our all new Apex Fit pattern The fins fell out of favor in the late 80's due to the quality of the original plastic fins A second screw in version of the fins was briefly used but it had another set of problems which let to the discontinuation of the fin boxes these fins used