Five years ago the use of Teflon tape was discussed on the ArgyllCMS list: http://www.freelists.org/post/argyllcms/2-white-reflectance-standard There is a spectral plot of a Teflon tape stack in SpectrumViz: http://www.pigment-print.com/spectralplots/spectrumviz_1.htm Measured on a stack of the tape 12mm wide and 9 mm thick. That is enough thickness for reflection. 19mm wide tape exists too, should improve sideways opacity. Cut the roll so the winding comes off as one piece, and fold that stack once or twice. Store in an old camera filter box or alike that presses the stack flat. From time to time peel off a tape layer to keep the top clean, it will not degrade etc by light etc but attracts dust. Polystyrene will degrade in time and attract dust. I use it together with a Color Checker passport. True, bending it so there is some difference in lighting on the surface makes it easier to set white balance, though in ACR you can still white balance and pull exposure afterwards as the Teflon sample will always give the highest reflection of all the objects captured. Overexposure in the take should be avoided. Met vriendelijke groet, Ernst Dinkla Dinkla Grafische Techniek Quad, piëzografie, giclée www.pigment-print.com