Abstract Properties of idealized silica—siloxane mixtures are described within the framework of a percolation process. Polymer chains are considered as bifunctional units of percolation. Silica particles are considered as units of percolation with a high functionality, f c ( f c ⋍ 10 2 ); f c is determined by the process of chain adsorption which results from the formation of hydrogen bonds with the silica surface. The state of gelation of a given mixture is characterized by using three variables: the initial specific amount of polymer Q i the specific amount of adsorbed polymer Q r, and the chain molecualr weight M ̄ n . A diagram is proposed to distinguish domains where an infinite cluster is formed from domains in which the clusters formed have a finite size. Expressions of the modulus of elasticity above the threshold of percolation are proposed.