In the vapour deposition method investigated, chemical reactions take place in an r.f. discharge instead of being promoted thermally. Glassy layers are deposited at 2-4μ/hr on cold or heated substrates. Materials prepared and evaluated include: (a) silicon from silane, (b) silicon dioxide from silane and nitrous oxide, (c) silicon nitride from silane and anhydrous ammonia. The method is expected to have a much wider application.