A thickening additive mixed with WEST SYSTEM Brand Epoxy to control the viscosity of the epoxy and prevent epoxy runoff in vertical and overhead joints. 406 is a very strong filler that creates a smooth mixture ideal for general bonding and filleting. It is also our most versatile filler. Often used in combination with other fillers it can be used to improve the improve strength abrasion resistance and consistency of fairing compounds resulting in a tougher smoother surface.