Porous Stone for Research Project

I am embarking upon a research project to develop a new Material (http://g654.org) . The Material (http://g654.org) must function at very high temperatures and (http://maplered.com) varying pressures. Prior research suggests that the Material (http://g654.org) must be permeable. Use of a porous additive has worked in the past.
I am thinking of using pumice, as I believe (but don't know) that pumice is very porous.

Because of the temperatures involved, I am interested in Stone (http://g603.net) Material (http://g654.org) s, such as pumice. But, I am open to any suggestions. Suggestions with a source of supply, for small quantities, would also be appreciated.

Thanks!