1) Interstellar ices are likely to be porous based on laboratory studies of amorphous solid water (ASW). 2) When porous ASW is heated, the pores collapse from cylindrical shapes to platelet shapes according to neutron scattering experiments. 3) Pore collapse begins around 117 K but is not auto-catalytic or accompanied by pore clustering below this temperature based on analysis of ice grown at 77 K.