West System® 406 Colloidal Silica Adhesive Filler. An epoxy thickening additive used to control the viscosity of the epoxy. Prevents epoxy runoff in vertical and overhead joints. Creates a smooth mixture, ideal for general epoxy bonding and filleting. Extremely strong and West System®'s most versatile epoxy filler. Often used in combination with other fillers. Can be used to improve the strength, abrasion resistance, and consistency of epoxy fairing compounds for a tougher, smoother surface. Designed for fillets, general bonding, abrasion resistance, structural fortification and thickening. Can be blended into any West System® 105 Epoxy Resin®/200 Series Hardener combination, West System® G/flex® 650 or West System® G/5® Five Minute Adhesive. Cures to an off-while color. Off-White. 5.5 oz.