CAS #: 63148-65-2. (Terpolymer of polyvinyl butyl, polyvinyl alcohol & polyvinyl acetate) Polyvinyl butyl resin for thin film support. Stronger than Formvar and more sticky, resulting in a firm attachment for slotted or meshed grids. The standard solution is 0.25% Butvar B-98 in Chloroform. Handley, D.A., et. al., Ultramicroscopy, 4,479 (1979).