  Many rare event searches including dark matter direct detection and
neutrinoless double beta decay experiments take advantage of the high VUV
reflective surfaces made from polytetrafluoroethylene (PTFE) reflector
materials to achieve high light collection efficiency in their detectors. As
the detectors have grown in size over the past decade, there has also been an
increased need for ever thinner detector walls without significant loss in
reflectance to reduce dead volumes around active noble liquids, outgassing, and
potential backgrounds. We report on the experimental results to measure the
dependence of the reflectance on thickness of two PTFE samples at wavelengths
near 178 nm. No change in reflectance was observed as the thickness of a
cylindrically shaped PTFE vessel immersed in liquid xenon was varied between 1
mm and 9.5 mm.
