As part of the prototyping process for the SoLID Heavy Gas Cherenkov detector (HGC), a suitable material must be chosen to be used as the entrance window. The HGC will be filled with gas at a differential pressure of 0.9 atm, or 13.2 psi (1.9 atm absolute) and must bulge less than 10 cm in order to fit within the SoLID assembly in Hall A at Jefferson Lab. In order to be certified for use, the window must meet these conditions under 2× operating conditions, i.e. 1.8 atm, (26 psi) differential pressure. In this series of tests it will be shown that a carbon fiber and Mylar window design meets these requirements.