Abstract: A composite substrate (10) is prepared for reinforcing a bituminous roofing material by securing together a carrier web (12) with a first set (14) of fiberglass rovings bundles and a second set (16) of fiberglass rovings bundles. The carrier web will have a pair of opposed planar surfaces. The web will define a machine direction and a cross machine direction for the substrate, with the first and second sets of rovings bundles each positioned in parallel relationship, with the longitudinal axes defined by the individual rovings of the two sets being in non-parallel relationship to each other when viewed normal to the plane of the web. The bundle sets are maintained in the spaced apart parallel relationships and the non-parallel angular relationship by the adhesive, stitching or other conventional method of securing which holds the substrate together. If a stitching machine is used, the preferred yarn (18) would be a polyester yarn.