A method and apparatus for forming a transversely curved or formed strip of material which can be cut to length for use in a fabric for coverings for architectural opening includes a supply role of a flexible fabric strip material that is sequentially passed through a heating chamber with an elongated upwardly convex extrusion across which the strip material is drawn and a cooling station before being wrapped on a take-up drum. The apparatus includes driven rollers about which the strip material passes and the strip material is exposed to tension detectors and controlled temperatures such that the strip material formed in the apparatus is uniform along its length.