In the poke-flow experiments, we used conditioning times of 20-22 h, 3-19 h, and 1-2 h, for RH values of 47-67%, 70-89%, and 90-97%, respectively. For RH values of 70-97%, the mixing time of water in the particles was shorter than the conditioning times, indicating the particles reached near-equilibrium conditions with the surrounding RH prior to poking (Section S4 and Table ).