What does the transitional phrase "consisting essentially of" do in a patent claim?

The transitional phrase "consisting essentially of" in a patent claim serves a specific function in defining the scope of the claim. This phrase indicates that the claim includes the specified ingredients or steps but allows for the inclusion of additional elements that do not materially affect the basic characteristics of the invention. This means that while the claim is centered on certain defined components, it is not strictly limited to only those components. This gives the patent a level of flexibility, while still emphasizing the importance of the core components identified in the claim.

By utilizing "consisting essentially of," the drafter can effectively protect an invention’s fundamental aspects while acknowledging that economically viable modifications or substitutions may be made without departing from the inventive concept. This approach is particularly beneficial in fields where variations may arise but do not change the essential nature of the invention being claimed.

In contrast, using the phrase "consisting of" would strictly limit the claim to the enumerated components, excluding any unlisted materials or steps, reflecting a narrower interpretation.