Reduced coating diameter fibers (RCDF) are attractive for increasing fiber density in cables due to their compatibility with the standard 125 μm clad diameter. In this paper, we review recent progress on RCDF and present new modeling and experimental results. We developed microbending models to quantify both the intrinsic and extrinsic microbending sensitivities. Modeling results show that RCDF have lower intrinsic microbending sensitivity but higher extrinsic microbending sensitivity. We made RCDF with coating diameters from 125 to 175 μm. The fibers showed good attenuation on shipping reel, which confirms modeling results on intrinsic microbending. We performed microbending tests on RCDF to quantify their extrinsic microbending sensitivity. The extrinsic microbending results suggest that the microbending sensitivity of RCDF can be reduced by using softer primary coating materials and bend-insensitive fiber designs. We studied the mechanical properties of RCDF including fiber proof strength and puncture resistance. Fiber proof tests showed that fibers with coating diameter greater than 160 μm could pass the 100 kpsi proof test at similar break rates to 242 µm. Fiber puncture resistance could be improved by using better coating material designs. We also conducted a cable trial on a loose tube cable using RCDF with 160 and 170 μm coating diameters. It showed that the RCDF could increase the fiber density by more than 2 times without any microbending and fiber handling issues. Finally, we studied thin 125 μm coated fiber for making low-loss connectors with direct ferrule insertion without stripping the coating, which is promising to reduce fiber breaks and improve connector long term reliability.