Cab-o-sil HS-5 Fumed silica Cabot Rheology Modifier/ Thickener >> Colloidal silicas Coatings Inks CAB-O-SIL® HS-5 untreated fumed silica is a synthetic, amorphous, colloidal silicon dioxide that is generally regarded as unique in industry because of its unusual particle characteristics. CAB-O-SIL fumed silica’s extremely small particle size, its enormous surface area, its high purity, and its chain forming tendencies set it apart in a class of its own. CAB-O-SIL fumed silica is a light, fluffy powder that is white in appearance and is used in many applications and a variety of industries. Rheology Control Reinforcement Free Flow Suspension Adsorbant Coatings Inks Synthetic, amorphous, untreated, fumed, colloidal silica. Used as a rheology control, reinforcement, free flow, suspension agent and adsorbant in coatings and inks. Offers very small particle size, very good surface area, high purity and chain forming tendencies.