West System 406 Colloidal Silica Adhesive Filler West Systems 406 Colloidal Silica is used as an epoxy thickening additive with 105 Resin Epoxy. It helps the user control the viscosity and prevent epoxy runoff. Perfect for vertical and overhead joints. A strong filler that creates a smooth mixture made for epoxy bonding and filleting. The most versatile filler from West System the 406 can improve strength, consistency, and abrasion resistance. This all combines to give you a tough yet smooth sur