Shrinkage at glass sphere loadings of 30% in nylon 66 is reportedly 70 to 80% less than in equivalent nonfilled or glass-fiber-filled versions. Warpage was reduced by 95 to 97%. High microsphere loadings also increase flexural modulus, abrasion resistance, and surface hardness. The spheres have a density of 2.5 gm/cm 3 , a crush strength of 30 kpsi, and a Mohs hardness of 6 to 6.5. They are nonporous and come in A-glass (soda-lime) and E-glass (borosilicate).

Potters Industries Inc., Box 840, Valley Forge, PA 19482, (610) 651-4715,