A method of forming a substrate in a thermal compression bonding process that permit substantially greater amounts of fillers than previously accomplished. The method employs a dispersion of a thermoplastic binder and a filler. The dispersion is then thermally compression bonded to form a substrate. Lightweight fillers are one example of fillers that are ideally suited for the thermal compression bonding through the use of a dispersion. Such lightweight fillers enable the formation of a substrate with a very low and desirable specific gravity.