As debate continues about whether to extend copyright protection to clothing design, the recent decision in Jovani Fashion v. Cinderella Devine explains why clothing has been denied copyright protection, although fabric design has been protected. The issue is functionality. Even the clearly creative elements of clothing design are so interwoven (pun intended) with the clothing’s function that clothing design typically fails both the physical and conceptual separability tests. The physical separability test, as its name suggests, concerns whether the creative elements literally can be separated from the utilitarian aspects of the work. The conceptual separability test concerns whether one can conceive of the creative elements apart from the useful ones.
If you are interested in further explanation of those tests and the copyrightability of useful articles. I recommend the Jovani Fashion case and cases cited therein, and Chapter 16 of Substantial Similarity in Copyright Law.