Metalized polypropylene film used in high energy density capacitors has been mechanically characterized to determine its elastic constants. The out of plane coefficient of thermal expansion (CTE) of the orthotropic film is 10 times as large as the smaller in plane CTE. The out of plane modulus is twice as large compared to one of the in plane moduli. The effect of interfacial pressure on the dielectric breakdown is also studied for the same film. It is observed that the dielectric strength of the film decreases at first and then increases above 4 MPa of compressive stress.