A three-dimensional preform, composite components formed with the preform, and processes for producing the preform and composite materials. The three-dimensional preform includes first and second sets of tows containing filaments. Each tow of the first set has a predetermined polygonal cross-sectional shape and is embedded within a temporary matrix. The preform is fabricated from the first and second sets of tows, in which the second set of tows are transverse to the first set of tows, adjacent tows of the second set are spaced apart to define interstitial regions therebetween, and the polygonal cross-sectional shapes of the first set of tows are substantially congruent to the cross-sectional shapes of the interstitial regions so as to substantially fill the interstitial regions.