Ratio of the vapor pressure above the sublimating ice to the tensile strength between constituting porous aggregates (radii are shown in the figure) as a function of the layer thickness (top panel for illumination corresponding to R_H = 1.243 AU, bottom panel R_H = 3.4 AU). Results are presented for water ice (dotted curves), carbon dioxide (dashed curves), and carbon monoxide (solid curves) ices.