A process and a spraying device for the filling of hollow spaces by the injection of solid substances in the form of fibres or granules with the aid of an air stream, wherein the solid substance is supplied as a suspension in a stream of primary air, which stream is, just before entering the space to be filled, mixed with an annular stream of secondary air moving roughly coaxially with the primary air stream, the secondary air stream being supplied tangentially relative to the primary air stream and under a pressure exceeding the primary air pressure, and wherein the spraying device consists of a supply section (1) and an outlet section, of which the supply section is provided with an inlet pipe (2) which has a substantially conical longitudinal section and a round cross-section, while the said supply section merges on a level with the smallest pipe diameter into an annular organ (4) which is provided on its outer circumference with grooves (5) crossing the long axis of the inlet pipe at an angle a.