Described are hydrophobic particulate inorganic oxides useful for reinforcing polymeric composition, e.g., rubber. The materials are characterized by: (a) the substantial absence of functional groups capable of chemical reaction with rubber; (b) a BET surface area of in the range of from 40 to 350 m²/g; (c) a hydroxyl content in the range of 2 to 15 OH/nm²; (d) a carbon content in the range of from 0.1 to 6 percent by weight that is substantially non-extractable; (e) a pH in the range of from 3 to 10; (f) an M1 Standard White Area less than 0.4 percent and (g) a methanol wettability of from 15 to 45 percent. Compositions such as polymers, cured organic rubber articles, master batches and slurries containing the hydrophobic fillers are also described.