Aerosil Fumed Silica 1 Quart. This is a thickening agent for epoxies, polyesters, and urethanes. You can thicken resins to your own liking by adding various amounts. This product is ideal for making adhesives and putties for gluing fiberglass, stone, wood, concrete, etc. This product makes cured resin more difficult to sand. This product is sold by the quart.