Polyvinyl Formal

An early insulation for magnet wire composed of the reaction product of polyvinyl formal (Formvar) and phenolformaldehyde. Later formulations were modified with the addition of materials such as melamine and isocyanate to improve specific wire properties. Polyvinyl formal insulated conductors are noted for their toughness and resistance to mechanical stresses. The film is quite resistant to softening and almost all varnish solvents and oils, but it must be stress relieved after winding into a coil to prevent crazing (microscopic cracking).