Formvar is a synthetic enamel composed of polyvinyl acetal and phenolic resins. Formvar's hot oil resistance sets it apart from all other magnet wire insulations. The flexibility, adhesion and abrasion scrape resistance of Formvar film is excellent. Its electrical properties are very good and it is resistant to common solvents. - While Formvar has been replaced by GP/MR-200 and Nytherm in many applications, Formvar continues to be the recommended film insulation most commonly used in oil-filled transformers.