Abstract: In the manufacture of reinforced composites having reinforcing filaments within a matrix, a filament consisting of a staple yarn spun from discontinuous fibers with low twist is subject to controlled stretching to vary the weight per unit length of the yarn along the length of the yarn. Apparatus for performing the stretching operation comprises two roll pairs spaced apart along the yard feed path and rotated at controlled relative speeds to obtain the desired elongation of the yarn. The yarn may be used directly in producing a composite, e.g., by applying resin to the yarn and winding it onto a mandrel or former, or it may be used to prepare a perform, prepeg tape, woven fabric or the like to be used in the production of a shaped composite. The invention makes it possible to vary the characteristics, e.g., thickness and/or strength, over a composite in a way not previously possible.