Low-density molding compound containing surface derivatized microspheres

A molded article comprising:

• a resin matrix having a surface;
• microspheroids having a mean diameter of from 16 to 45 microns in said resin matrix, said microspheroids consisting of acid cleaned glass microspheroid surfaces to increase the number of the surface activating agent per unit of microspheroid surface area, said microspheroids having a specific gravity of between 0.15 and 0.6 and an isotactic crush strength of greater than or equal to 2750 kilopascals (kPa);
• a plurality of surface activating agent molecules covalently bonded to each of said acid cleaned glass microspheroid surfaces _in an amount to form between 0.1 to 1 monolayer on each of said glass microspheroids, said plurality of surface activating agent molecules being alkoxysilanes;
• filler particles in said resin matrix;
• and
• fibers in said resin matrix, wherein the article has a specific gravity of between 0.80 and 1.25 and passes a gravel test according to SAE J400.