The electrical, optical, and mechanical properties of porous methylsilsesquioxane (MSQ) films created using two different sacrificial polymers: trimethoxysilyl norbornene (TMSNB), and triethoxysilyl norbornene (TESNB) were evaluated in this study. The introduction of porosity lowered the dielectric constant, the index of refraction, and the elastic modulus and hardness of the films as compared to the nonporous MSQ films. The dielectric constant was lowered from 2.7 for a pure MSQ film to 2.35 for a film with 30 wt % initial concentration of TMSNB. Similarly, the index of refraction was lowered from 1.42 to 1.30 for a 30:70 wt % TMSNB: MSQ film. The TMSNB: MSQ films showed a transition from closed-to-open cell porosity in the range from 20 to 30 wt % loading of sacrificial polymer as determined from positron annihilation spectroscopy. Improvements in the fracture toughness were observed for the TESNB: MSQ films as compared to the pure MSQ or TMSNB: MSQ films.