A novel glass fiber mat is described herein. The mat includes a plurality of substantially uniformly enmeshed individual filament fibers which comprise at least 70% by weight of the fibrous component of the mat. The mat is further characterized in that less than 20% of the area of the mat are voids which extend through the thickness of the mat, the rest being fibrous material, of said voids, at least 80%, 30% and 10%, have an equivalent diameter whose size is less than about 50 microns, 10 microns and 5 microns, respectively. This mat has an exceedingly high tensile strength both in the machine and the cross-machine directions.