The compressive strength (filling factor φ versus pressure p) as obtained from experiments. The dark shaded region with the solid line fit refer to the omnidirectional compression experiment performed by Güttler et al. (2009) whereas the light shaded region and the dashed line fit were obtained for unidirectional compression by Blum & Schräpler (2004). The small image on the top left depicts the experimental setup of the omni-directional compression experiment. (Figure taken from Güttler et al. 2009.)