Ergonomic road and gravel saddle designed to effortlessly follow pelvic movements, reducing pressure on sit bones BASF Infinergy closed cell particle foam core and Orthopedic AirCell Foam padding absorbs road shock and reduces stress on lower back Floating TwinShell design dampens shock before it reaches lower back Rearward positioned and anatomically adapted pressure relief channel prevents discomfort and numbness SR Allroad Pro Carbon: Carbon composite shell with Orthopedic AirCell foam SR Pro: Carbon composite shell with Orthopedic AirCell foam SR Comp: Nylon composite shell with orthopedic comfort foam with OrthoCell pads Recommended sizing for sit bone width: S/M 912cm, M/L 12-16cm