Abstract: A fiber filler for filling voids between mated fiber plies, for example, as occurs in the preparation of a preform assembly for forming a T-shaped structural member, is disclosed. The fiber filler comprises a plurality of unidirectional fibers, shaped to conform to the shape of the void and a stabilizer intermingled with the unidirectional fibers. The stabilizer is present in an amount sufficient to hold the fibers together in the shape of the void, but below an amount which would inhibit resin flow during subsequent injection, so that the fiber filler is fully integrated into the final part.