Trade dress cannot be registered as a trademark if it is functional. Registration of trade dress will be refused as functional if it is essential to the use or purpose of the product or it affects the cost or quality of the product. The reason for refusing registration of functional trade dress is to maintain a balance between trademark law and patent law, the latter being used to protect products having some patentable function.
Trade dress also cannot be registered unless it is distinctive. Distinctiveness is evaluated depending upon whether the trade dress is the product design or the product packaging. Product design is considered as never being inherently distinctive. In this case, the only way to register the product design as a trademark (on the Principal Register, as opposed to the Supplemental Register) is to show “acquired distinctiveness” or “secondary meaning,” which is basically a showing that consumers associate that product design with the particular manufacturer of the product. Such acquired distinctiveness can be shown by “substantially exclusive and continuous use” of the product design by the applicant in commerce for five years prior to the application for registration. On the other hand, product packaging may be inherently distinctive; however, if not, it too may be registered by making the same showing of acquired distinctiveness.
Of course, the foregoing is simply a general overview. The actual analysis of whether trade dress can be registered as a trademark at the U.S. Patent and Trademark Office can be complicated. Accordingly, evaluation of the registrability of the proposed trademark should be done prior to filing a trademark application.

