The invention relates to a radiation curable composition including a polyester urethane (meth)acrylate oligomer prepared from ortho-carboxylic polyester polyols, where the composition, after cure, has a secant modulus greater than about 600 MPa and an elongation at break of at least about 10%. The invention also relates to coated optical fibers and optical fiber ribbon including at least one coating derived from this composition, and to a process of making these coated optical fibers.