An optical fiber unit for air-blown installations includes a number of optical conductors, a first layer of resin material, a second layer of resin material radially outer to the first layer of resin material and a sheath of a thermoplastic material, wherein the second layer of resin material has a secant modulus higher than a secant modulus of the first layer of resin material and wherein the sheath of thermoplastic material is over and in close contact with the second layer of resin material.