  The Gemini Planet Imager (GPI) has been designed for the direct detection and
characterization of exoplanets and circumstellar disks. GPI is equipped with a
dual channel polarimetry mode designed to take advantage of the inherently
polarized light scattered off circumstellar material to further suppress the
residual seeing halo left uncorrected by the adaptive optics. We explore how
recent advances in data reduction techniques reduce systematics and improve the
achievable contrast in polarimetry mode. In particular, we consider different
flux extraction techniques when constructing datacubes from raw data, division
by a polarized flat-field and a method for subtracting instrumental
polarization. Using observations of unpolarized standard stars we find that
GPI's instrumental polarization is consistent with being wavelength independent
within our errors. In addition, we provide polarimetry contrast curves that
demonstrate typical performance throughout the GPIES campaign.
