An optical fiber having an internal glass portion, a first coating layer surrounding the glass portion and a second coating layer surrounding the first coating layer. The first coating layer is formed from a cured polymeric material obtained by curing a radiation curable composition having a radiation curable oligomer having a backbone derived from polypropylene glycol and a dimer acid based polyester polyol. The cured polymeric material has: (a) a hardening temperature (Th) from -10.degree. C. to about -20.degree. C. and a modulus measured at the Th lower than 5.0 MPa; or (b) a hardening temperature (Th) from -20.degree. C. to about -30.degree. C. and a modulus measured at the Th lower than 20.0 MPa; or (c) a hardening temperature (Th) lower than about -30.degree. C. and a modulus measured at the Th lower than 70.0 MPa.