How does the phrase “consisting essentially of” differ from “comprising” and “consisting of” in patent claims?

This page is an FAQ based on guidance from the Manual of Patent Examining Procedure. It is provided as guidance, with links to the ground truth sources. This is information only: it is not legal advice.

The phrase “consisting essentially of” occupies a middle ground between the open-ended “comprising” and the closed “consisting of” in patent claims. According to MPEP 2111.03:

“The transitional phrase “consisting essentially of” limits the scope of a claim to the specified materials or steps “and those that do not materially affect the basic and novel characteristic(s)” of the claimed invention.”

Key differences:

• “Comprising”: Open-ended, allows for additional, unrecited elements.
• “Consisting of”: Closed, excludes any element not specified in the claim.
• “Consisting essentially of”: Partially open, allows only those additional elements that do not materially affect the invention’s basic and novel characteristics.

For example, “A cleaning composition consisting essentially of ingredients X, Y, and Z” would allow for minor additives that don’t significantly change the cleaning properties, but would exclude major components that alter its fundamental nature.

When using or interpreting “consisting essentially of,” it’s important to refer to the specification to understand what constitutes a material change to the invention’s basic and novel characteristics.