A system is provided for aesthetically covering access openings in a tub skirt when access to the interior of the skirt is not required. The method of making the copolymers involves reacting a diamine with a precursor having at least one polydiorganosiloxane segment and at least two oxalyamino groups. The filter is in fluid communication with the module inlet and the module outlet. Thereby, a meeting portion is formed in the vicinity of a boundary between the seed crystal portion and the mask in a thickness direction of the GaN layer.