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The direct voltage electric strengths of several polymers are measured using a new type of environmental chamber in which a new specimen of the material can be introduced without the necessity of cooling and reheating after every voltage application. The range of temperatures at which investigations are carried out is 23°C-250°C. The plots of the dielectric strength on Weibull paper demonstrates departure from the two parameter Weibull distribution, particularly at low field strengths. In each case the method of determining the more favorable distributions are discussed with the view of obtaining consistent results for the dielectric strength. The lower voltage breakdown cannot be ignored if high reliability is desired and the evaluated dielectric strengths on this basis are also presented. The polymers studied are aromatic polyamide, PTFE, aromatic polyimide and polyamide-polyester-polyamide composites. Thickness effects are presented for selected polymers.