Whenever clients learn that a utility patent application will cost about 10 times that which a design patent application costs, they immediately declare their invention to be a new design! Sure, most inventions are/include a 'new design' – in the sense of the English word 'design'. But unfortunately not in the patent office definition for 'design' – the same word with a totally different meaning. Nearly always, these inventors require a utility patent application rather than a design patent application – two very distinctly different things.
For purposes of patent law, 'design' means that an invention is purely aesthetic. The appearance of the matter being patent is pleasing and valuable – but only the attractive appearance is protected without regard for function nor use. Design patents are good for product which take a particular shape and form with looks cool or otherwise attractive. Sometimes, Nike company will patent the look of a shoe upper – in most cases, a shoe upper performs the same as any other shoe upper – but when its look is special according to Nike and they don't want others making and selling shoes which look the same, then they get a design patent.
A cool looking tire tread may be patented. However, if the tire tread actually has a functional nature, only the look will be protected. If someone devises another tread having identical function but a different look, it won't be protected by the patent. In this regard, very little 'overlap' is available. In almost every case, a design patent will be wholly ineffective to protect the function and use of an invention. Only when the function and use arises from the aesthetic nature of the system will a design patent tend to cover function. This is a very limited set.
Many folks attempt the design patent to save money and to legitimize writing 'Patented' on their products – presumably to warn potential competitors. Strictly speaking, this strategy might push back some unsophisticated competition. However sophisticated product manufacturers and marketers will not be afraid. If they want to copy your invention, they won't hesitate to make a product with a different design and compete with you directly. Your design patent will do little or nothing to stop sophisticated competition.
A design patent has little or no written description. Usually comprised of just a few drawings and a very simple claim(s) which refers to the drawings. That's it. One can pretty much gain a full understanding of the look of something by considering one simple drawing. Here are a few examples of some nice design patents:
Nike Shoe Upper Design Patent –
Goodyear Tire Design Patent
Siemens Dishwasher Display (Icon) Patent