The issues of finding better methods for designing molds taking into account the thermal deformations of parts and assembly units are considered. The existing methods of designing molds for plastics have been developed for a long time. They are focused more on products of mechanical engineering, electrical engineering, microelectronics, etc. Thermal deformations in these methods are generally not taken into account. However, the increase in accuracy requirements, if desired, to increase the productivity of the process leads to the fact that in some cases these deformations become comparable with the tolerance for design dimensions. This paper presents the results of theoretical and experimental studies on methods for assessing thermal deformations, design diagrams, and finding areas for which this accounting and adjustment of methods are necessary.