Formed by mixing isocyanate and a polyether polyol containing a halogenated hydrocarbon agent. Mixing releases heat, causing the foam to expand as much as 30 times the original volume of the liquid. The foam, which becomes cellular and rigid within minutes, is heat resistant and essentially impervious to air and water, and has substantial binding strength. Its characteristics suggest possible uses in mining for insulation, stoppings to control ventilation, and seals to control water and to consolidate broken ground.