An optical fiber is disclosed that includes a primary coating formed from a radiation curable composition that includes a curable cross-linker essentially free of urethane and urea functional groups, a curable diluent, and a non-radiation curable component comprising (thio)urethane and/or (thio)urea groups. The primary coating features low Young's modulus, low Tg, and high tensile strength. The optical fiber exhibits low microbend losses in wire mesh drum and basketweave tests.