Molecular sieve 3A (zeolite)
A zeolite powder that locks water inside its pores, keeping polyurethane B-sides dry without releasing any gas.
Molecular sieve 3A is a synthetic potassium aluminosilicate zeolite with uniform pores about 3 ångströms across, small enough to admit water molecules but exclude most larger molecules. It is supplied as a powder or as a paste dispersed in castor oil or another carrier.
It is dispersed into polyols, B-side blends, sealants and polyurethane elastomers to absorb moisture from raw materials and humid air, preventing CO₂ bubbles and foaming when the isocyanate is added.
Water is physically adsorbed in the zeolite cavities and held tightly, so unlike chemical scavengers no gas is released. The small pore size means it takes up water selectively without absorbing most solvents or reactants.
The powder is dusty and absorbs moisture with heat release; avoid inhalation and eye contact. Keep sealed until use to preserve capacity.
The smaller 3A pores admit water but exclude larger molecules, reducing unwanted adsorption of other formulation ingredients.
Typically a few percent of the component, depending on expected moisture. Follow formulation guidance.
