The invention relates to coating or otherwise modifying or changing a surface characteristic, including a surface characteristic of a device for administering an injectable product, wherein the device includes a casing made of multiple casing parts, wherein at least one external surface of at least one of the casing parts is completely or partially provided with one or more surface-refining coatings. The coating may be applied to the casing part after or while the casing part is shaped, and the coating may comprise various materials which may be arranged alongside each other, on top of each other or may be mixed.