A method of thermally insulating pipe comprises rotating the pipe at a uniform speed about a substantially horizontal axis while applying a polyurethane foam mix to the surface of the pipe progressively along its length, simultaneously forming a metal tube of larger diameter than the pipe, the tube being progressively extended coaxially with the pipe and progressively enveloping the newly coated surface of the pipe, and maintaining the pipe at a temperature at which the mix constituents will react to form a foamed mass enveloping the pipe and filling the space between the pipe surface and the tube.