From the images recorded when the SOA material flowed, we determined the time required for the inner diameter of the half-torus shape to reduce by ~50% of its initial value, which we term the experimental flow time τ exp,flow . For RH values ≲ 60%, the particles cracked and did not flow during the observation time (e.g. Fig. , 1 st row). In these cases the observation time was used as a lower limit to τ exp,flow .