The results obtained with PTFE and PMMA plates are
more critical. For PTFE, in vitro SPF/Label correlation seems to be
different for low and high SPF values; it has been already
demonstrated that better results are obtained when a smaller
amount of sunscreen is applied [15]. In case of PMMA, SPF values
have been calculated assuming that the substrate used for A(l)
recovering was with or without glycerine; results were almost
equivalent.