Rea Round single build aluminum magnet wire designed for continuous operation at 105 °C, Formvar was one of the first magnet wire insulations based on synthetic materials. Today, Formvar is still widely used in oil-filled transformers as well as demanding cryogenic applications. Excellent hydrolytic stability. - Rea Formvar round single build aluminum magnet wire is a film insulation composed of modified polyvinyl acetyl resins. Designed for continuous operation at 105 °C, Formvar was one of the first magnet wire insulations based on synthetic materials.