You searched for: “closed pores”
closed pore (s) (noun), closed pores (pl)
A cavity inside a material that is impermeable when the material is immersed in a liquid: Closed pores can be contrasted to open pores, or the spaces between particles, cracks, and capillaries that extend into materials from their surfaces.

Impermeable refers to a situation that does not permit the passage of liquid, gas, or other fluids to take place.