  Polytetrafluoroethylene (PTFE) is an excellent diffuse reflector widely used
in light collection systems for particle physics experiments. In noble element
systems, it is often coated with tetraphenyl butadiene (TPB) to allow detection
of vacuum ultraviolet scintillation light. In this work this dependence is
investigated for PTFE coated with TPB in air for light of wavelengths of
200~nm, 260~nm, and 450~nm. The results show that TPB-coated PTFE has a
reflectance of approximately 92\% for thicknesses ranging from 5~mm to 10~mm at
450~nm, with negligible variation as a function of thickness within this range.
A cross-check of these results using an argon chamber supports the conclusion
that the change in thickness from 5~mm to 10~mm does not affect significantly
the light response at 128~nm. Our results indicate that pieces of TPB-coated
PTFE thinner than the typical 10~mm can be used in particle physics detectors
without compromising the light signal.
