A molecular sieve is a material with pores (very small holes) of uniform size. These pore diameters are similar in size to small molecules.
Molecular sieves are used for drying gases and liquids and for separating molecules on the basis of their sizes and shapes. When two molecules are equally small and can enter the pores, separation is based on the polarity (charge separation) of the molecule, the more polar molecule being preferentially adsorbed.
Molecular sieves are crystalline, hydrated aluminosilicates of (most a column of 0.53-mm diameter and 50-m length coated with molecular sieves of 5A .