FOAM AND GLASS

Understanding Materials

In the liquid state, matter flows, whereas solids are rigid. As they cool, liquids solidify either into crystals with the molecules arranged in regular lattice arrays, or into glasses with the molecules arranged randomly. Foams, such as shaving cream, share properties with both liquid and solids: Though 92% gas and 8% liquid, foams, like solids, hold their shapes and do not flow. However, when subjected to shear forces (opposing forces applied at different heights) foams flow like liquids.
-Andrea Liu, Professor of Chemistry at the University of California, Los Angeles.