Fractional polarization versus physical resolution of the observation for double radio relics. Each marker represents a single relic. Circles are average fractional polarization computed integrating over the polarized regions of the relic, downward triangles are the maximum values (therefore one relic can have both measurements in the plot). Arrows are upper limits computed for relics where we did not detect polarization. The color-scale represents the projected distance of the relic from the X-ray peak of the hosting galaxy cluster.