Fiber tows including a heat-activatable sizing are described. The sizing compositions have a first modulus at 25° C. of at least 150 megapascals (MPa) and no greater than 400 MPa; and a second modulus of 100,000 pascals (Pa) at a temperature of no greater than 160° C. Methods of preparing articles from such sized fiber tows and the articles comprising such sized fiber tows, including unidirectional and bidirectional constructions are also described.