Fan blade platform includes axially extending I beam supporting radially outer skin having flowpath surface. I beam includes upper and lower or radially outer and inner I flanges on radially outer and inner beam ends of axially extending I web. Radially outer skin on top of and bonded or otherwise attached to radially outer I flange. I beam may be integral and monolithic and made from a non-metallic composite or thermoplastic material and have post cure formed weight relief holes. I beam may include oppositely facing or back to back first and second C beams. First C beam including axially extending first C web disposed between radially outer and inner first C flanges. Second C beam including axially extending second C web disposed between upper and lower or radially outer and inner second C flanges. I beam may be asymmetrical about center plane of I web.