Many substances are added to Carpet Backing or Polyurethane.  Dehydrating agents such as molecular sieves 3A and 4A are used regulate water content. Preferably these materials are incorporated in the polyol blend.  Generally, all ingredients except the isocyanate are preblended into the polyurethane matrix. This is commonly called the polyol blend. The isocyanate is sensitive to water and is thus removed by the molecular sieves.

3A molecular sieve does not adsorb gases that would be later cause bubbles and surface defects.  4A molecular sieve can be added to the resin/solvent system under vacuum to remove any displaced gasses.  In polyurethane systems, approximately 1-2% of the matrix is based on molecular sieves.