Flame polishing is a method of polishing a material, usually thermoplastic or glass, by exposing it to a flame or heat. By melting the surface of the material, surface tention smooths the surface out. Operator skill is critical with this method. When done properly, flame plastic polishing produces the clearest finish, especially acrylic. This method is most applicable to flat external surfaces. Flame polishing is frequently used in acrylic plastic fabrication because of its high speed when compared to abrasive methods.