The 6.6 x 6.6" Ultra Contrast 2 Filter from Tiffen helps to open your shadows by using the ambient light surrounding the image area as well as the light in the actual image itself. It lowers contrast uniformly throughout, with little or no loss of sharpness within the scene, even where there are varying degrees of brightness.
Shadow areas will reveal more detail but without any flare or halation from direct light sources or bright reflections. The Ultra Contrast works similar to a Tiffen Low Contrast filter with the difference being that it reduces contrast throughout the entire image whereas a Low Contrast filter will only open the shadows.
The #2 Ultra Contrast filter continues to capture even more detail in the shadow areas. Contrast continues to be lowered evenly throughout the image area. Sharpness is still not compromised nor will you begin to see any flare or halation.
Tiffen's ColorCore glass is produced through a process that entails permanently laminating the filter material in between two pieces of optical glass that are ground flat to tolerances of a ten-thousandth of an inch, then mounting them in precision aluminum rings.