In the COLIPA guideline for the in vitro determination of UVA
protection factor [4], an application rate of 0.75 mg/cm2 is indicated
for PMMA plates used for UVA labelling; this amount could also be
evaluated for SPF determination. In our laboratory, we are also
testing PTFE with different rate of applications. So far, we have
obtained a good correspondence between in vitro and label values
with an amount of 0.65 mg/cm2. From the results reported above,
it is possible to conclude that different substrates can be suitable
for in vitro SPF evaluation, but a calibration must be performed in
order to define the regression curve. Calibration should be
performed by each laboratory, since the result depends on method
and instrumentation used. Calibration should be performed also