What is the difference between “consisting essentially of” and “comprising” 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.

What is the difference between “consisting essentially of” and “comprising” in patent claims?

The transitional phrases “consisting essentially of” and “comprising” have different effects on the scope of patent claims:

• Comprising: This is an open-ended phrase that allows for additional, unrecited elements or steps.
• Consisting essentially of: This phrase limits the scope of a claim to the specified materials or steps and those that do not materially affect the basic and novel characteristics of the claimed invention.

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.“

While “comprising” allows for any additional elements, “consisting essentially of” only permits additional elements that don’t fundamentally change the nature of the invention. This distinction can be crucial in determining the scope and patentability of claims.