Molecular sieve 3A is type A zeolite, also called zeolite 3A.Molecular Sieves 3A is an alkali metal alumino-silicate.  It is the potassium form of the type A crystal structure. Type 3A has an effective pore opening of about 3 angstroms (0.3 nm). The molecular sieve’s adsorption capacity will depend on the pore size and pore volume of the molecular sieve. This size is large enough to allow in moisture, but excludes molecules such as unsaturated hydrocarbons which can potentially form polymers;