Method for preserving cavities, having the following features: a. the method serves for the application of a protective layer composed of a cavity-preserving agent to the inner side of a hollow body, in particular to the inner side of a motor vehicle part, and, b. for the purpose of the application, use is made of a mixing nozzle unit which is coupled by way of a proximal end to a rotor unit, by means of which said mixing nozzle unit can be rotated about an axis of rotation, wherein, at a distal end, the mixing nozzle unit has a mixing nozzle which is oriented radially with respect to the axis of rotation, and c. the mixing nozzle unit has two separate feed channels (70, 72), extending in the direction of the axis of rotation, for the cavity-preserving agent and for gas for the purpose of the atomization of the cavity-preserving agent, wherein the cavity-preserving agent and the atomization gas are conducted separately through the feed channels (70, 72) as far as the mixing nozzle, and d. the mixing nozzle unit is moved into the hollow body through an opening of the hollow body in the direction of the axis of rotation such that at least the mixing nozzle is situated within the hollow body, and e. the cavity-preserving agent is discharged in atomized form by means of the mixing nozzle and is deposited on the inner side of the hollow body, wherein, during the discharge or between multiple discharge phases, the mixing nozzle unit is rotated about the axis of rotation in relation to the hollow body, characterized by at least one of the following further features: f. while the mixing nozzle unit is being rotated, the feeding of cavity-preserving agent to the mixing nozzle is varied, with the result that the quantity of cavity-preserving agent that is discharged over an angular range of constant size is non-uniform in a manner dependent on the rotational position, and/or, g. while the mixing nozzle unit is being rotated, the feeding of cavity-preserving agent is interrupted in phases such that no cavity-preserving agent is discharged in a sub-region of the circumference, and/or h. the mixing nozzle unit is rotated at a varying rotational speed, with the result that the quantity of cavity-preserving agent that is discharged over an angular range of constant size varies in a manner dependent on the rotational position. a. the method serves for the application of a protective layer composed of a cavity-preserving agent to the inner side of a hollow body, in particular to the inner side of a motor vehicle part, and, b. for the purpose of the application, use is made of a mixing nozzle unit which is coupled by way of a proximal end to a rotor unit, by means of which said mixing nozzle unit can be rotated about an axis of rotation, wherein, at a distal end, the mixing nozzle unit has a mixing nozzle which is oriented radially with respect to the axis of rotation, and c. the mixing nozzle unit has two separate feed channels (70, 72), extending in the direction of the axis of rotation, for the cavity-preserving agent and for gas for the purpose of the atomization of the cavity-preserving agent, wherein the cavity-preserving agent and the atomization gas are conducted separately through the feed channels (70, 72) as far as the mixing nozzle, and d. the mixing nozzle unit is moved into the hollow body through an opening of the hollow body in the direction of the axis of rotation such that at least the mixing nozzle is situated within the hollow body, and e. the cavity-preserving agent is discharged in atomized form by means of the mixing nozzle and is deposited on the inner side of the hollow body, wherein, during the discharge or between multiple discharge phases, the mixing nozzle unit is rotated about the axis of rotation in relation to the hollow body, f. while the mixing nozzle unit is being rotated, the feeding of cavity-preserving agent to the mixing nozzle is varied, with the result that the quantity of cavity-preserving agent that is discharged over an angular range of constant size is non-uniform in a manner dependent on the rotational position, and/or, g. while the mixing nozzle unit is being rotated, the feeding of cavity-preserving agent is interrupted in phases such that no cavity-preserving agent is discharged in a sub-region of the circumference, and/or h. the mixing nozzle unit is rotated at a varying rotational speed, with the result that the quantity of cavity-preserving agent that is discharged over an angular range of constant size varies in a manner dependent on the rotational position.