Studying debris disks is one of the frontiers of exoplanet science because observations of these objects provide direct constraints on planetary system formation and planet migration around other stars. To date, twenty-four debris disks have been spatially resolved in scattered light, revealing the location of the dust and the albedos of the grains when compared with thermal emission measurements. Although these observations help break some of the degeneracies between composition, size, porosity, and shape, the detailed grain properties are still not well understood. A key limitation is that the previous generation of instruments lacked the contrast and image fidelity to detect dust disks within a ~1.5 arcsec radius. Therefore the thermally emitting dust detected close to the star is not the same cold grain population detected by scattered light observations far from the star. We propose to obtain Gemini Planet Imager (GPI) Integral Field Spectroscopy (IFS) and Polarimetry of all of the debris disks spatially resolved in scattered light observable from Gemini South. GPI offers an unprecedented discovery space by virtue of its small inner working angle and sensitivity using dual channel polarimetry. IFS observations will be sensitive to spectral features and better constrain the color of the scattered light and therefore the particle composition and size. Polarimetry will allow us to break the degeneracy in forward scattering between particle size and porosity. Our team will combine the proposed GPI observations with complementary high contrast imaging and thermal mapping data from HST, MagAO, and ALMA to develop holistic models that will significantly improve our understanding of the materials available during the late stages of planetary system formation.