Porous solids are abundant in the world. Examples include activated carbon, zeolite, and metal-organic frameworks (MOFs). Solid electrolytes in next-generation batteries have ion migration channels and hence are porous solids in a broad sense. Because the properties of porous solids are dictated by pore size, the way the pores are connected internally, and the chemical nature of the pore walls, achieving high degrees of freedom in designing these properties is crucial.