  The performance of a detector using liquid xenon (LXe) as a scintillator is
strongly dependent on the collection efficiency for xenon scintillation light,
which in turn is critically dependent on the reflectance of the surfaces that
surround the active volume. To improve the light collection in such detectors
the active volume is usually surrounded by polytetrafluoroethylene (PTFE)
reflector panels, used due to its very high reflectance -- even at the short
wavelength of scintillation light of LXe (peaked at $178\,\text{nm}$). In this
work, which contributed to the overall R\&D effort towards the LUX-ZEPLIN (LZ)
experiment, we present experimental results for the absolute reflectance of
three different PTFE samples (including the material used in the LUX detector)
immersed in LXe for its scintillation light. The obtained results show that
very high bi-hemispherical reflectance values ($\geq97$%) can be achieved,
enabling very low energy thresholds in liquid xenon scintillator-based
detectors.
