Molecular sieves, a group of space age chemicals known as zeolites, have outstanding filtration abilities. Their chemical structure is a narrow, rigid, and uniform crystalline lattice which has such precise pore size that it restricts movement of substances on the basis of molecular size! Small molecules, like water, can enter the lattice, but are trapped therein, thus the name "molecular sieve". Molecular sieves are highly effective filtrants for moisture, nitrogen oxide, oil vapor, and limited amounts of carbon monoxide and carbon dioxide. Variety 13X is the best formulation for processing divers' air because it is designed to trap water vapor. Packaged in 1 gal., 6.5 lb bottles.