(1) A relatively non-adhesive substance added to an adhesive to improve its working properties, permanence, strength, or other qualities. (2) A substrate used to take up air space to prevent shifting of other items in a container. (3) Fillers are additives used in paper manufacture that fill the gaps between the paper fibers and enhance opacity, whiteness, and smoothness. The most common fillers are mineral compounds such as kaolin or calcium carbonate; they are generally added to the liquid pulp mass. In finished papers, the filler content can be as high as 35 percent.