Clay and Pumice have pores but the pores are not well connected. If you poured water over either of them it would just run off the surface. It wouldn't run through. But they could hold water in their pores. We can say then that both or them ARE but NOT .

Clay and Pumice can both be said to be Porous but they are not Permeable

Explanation:

A porous substance is one which have pores in in through which air or liquid can pass through. Both clay and pumice are porous due to the presence of pores in them. These pores allow air to pass through them. However, since the pores are not well connected water do no pass through them. As a result, clay vessels can hold water within them and pumice floats on water.

Permeability is the ability of a substance to allow other substances to pass through. Both clay and pumice have low permeability, as a result they do not allow water to pass through them. Rather, water runs over their surface when poured over them.