Vacuum Pressure Impregnation, or “VPI,” is a process where porous materials are sealed together using resin or varnish. They are connected using pressure and a vacuum. The VPI process is designed primarily for use in high-voltage generators and motors. It is used to create void-free insulation in a variety of different devices. Vacuum Pressure Impregnation follows a multi-step process. The process begins with preheating, followed by dry vacuuming, filling, wet vacuuming, pressure, draining, and curing. This process prevents varnishes from losing their volume. If the process is performed correctly, VPI can prevent volume loss by 50 percent.