Humidity has a nominal effect on the dielectric strength of Mylar. Figure 3
illustrates that for 7.5 mil film, varying the relative humidity from 20% to 80%
causes less than a ±10% change in dielectric strength from the value obtained at
the target rate of 35% relative humidity (ASTM D-149 and ASTM D-2305).
Figure 3: Dielectric strength at various humidities
Dielectric