Polarization fraction as a function of wavelength for the different dust models tested with SKIRT assuming the scattering medium consists of a polar outflow. Left panel: Expected polarization fraction for bipolar cones for a number of different dust mixtures. Right panel: Expected values for single approaching or receding cones for the preferred dust mixture. The green circle shows the measurement for W0204–0506 in the R_Special band. The horizontal error bar shows the width of the photometric band.