Abstract: A thermoplastic material, such as a sheet of polystyrene or polyethylene m, is placed between a trim guide, which may be a die, mold or press, and is in the form of at least two heat-conducting metal pieces, one of which is movable towards the other. The trim guide is pressure-operated to pressurize the material along the area to be trimmed. This may be an edge of a plastic sheet, the perimeter of an article produced from the material, or may be holes or slots to be cut in the material. A trim tool, heated to a temperature high enough to melt the material, is then moved along the trim guide. The trim tool melts or vaporizes the pressurized material along the trim guide, which creates a definitive point at which melting or vaporization of the material stops. The trim guide is made from metal having high heat-conductivity, such as aluminum which has sufficient heat-conductivity to create a point at which melting, caused by the trim tool vaporizing the material, stops.