The series of papers, of which this is the first, aims to demonstrate the importance of chemical reactions between filler particles and elastomer matrix in determining the physical properties of filled elastomers. A model system comprising small glass beads as the filler and crosslinked poly (ethyl acrylate) as the elastomer has been used. The beads themselves are inert towards the matrix during polymerization, but the reactivity of the surfaces of the beads can be varied by suitable treatments. This paper describes techniques for fractionating the beads to give narrow particle-size distribution, for preparing unfilled and filled elastomer sheets, and for preparing composites in which an elastomer sheet is polymerized in contact with a glass plate which may or may not have been previously subjected to surface treatment.