While nanocrystalline diamond is quickly becoming one of the most widely studied nanomaterials, achieving a large fraction of diamond nanoparticles in a polymer coating has been an unresolved problem. In this work, polymer nano- and microfibers containing high loadings of 5 nm diamond particles (up to 80 wt % in polyacrylonitrile and 40% in polyamide 11) have been demonstrated using electrospun nanofibers as a delivery vehicle. The electrospun nanofibers with a high load of nanodiamond in the polymers were fused into thin transparent films, which had high mechanical properties; an improvement of 4 times for the Young's modulus and 2 times for the hardness was observed already at 20% nanodiamond in polyamide 11. These films can provide UV protection and scratch resistance to a variety of surfaces, especially in applications where a combination of mechanical, thermal, and dielectric properties is required.