In many uses of liquid resins, it is desirable to reduce the weight of the finished product. One way to reduce the weight below the original resin weight is to incorporate a suitable additive. Hollow phenolic microspheres are excellent for use in a variety of industrial applications. They are lightweight, chemically inert, and mechanically strong. They can be excellent adhesives, gap filling formulations, sandable putties, syntactic foams, and molded and laminated structures that must be lightweight and strong. About 30% by weight will make most resins unpourable. Filling casting are quite machinable; turns casting brown.