The phrase "material substance" refers to something that is physically present and can be touched or observed. It refers to things that have a physical form and can be sensed through our five senses. Full definition
It destroys the notion of material substance and substitutes that of an event in which ~ the many become one, and are increased by one. (religion-online.org)
Yet if you were to focus on the book's material substance with an atomic microscope, you would see that you are holding nothing. (goodreads.com)
In his paintings from the period words are made of the same material substance as images. (galleriesnow.net)