Abstract: A thermally-insulating, non-flammable, air-permeable insulation for installation in the field, for example, in closed cavities between the walls of a house. A multitude of individually preformed, foamed plastic particles are initially entrained in a carrier stream, and thereupon drenched with a settable film-forming, non-flammable, liquid substance, such as a sodium silicate solution. The liquid substance sets to form a film which covers and adheres the particles to one another to form a thermally-insulating dense structural aggregate mass having structural integrity, resistance to fire, and venting capability. A method of making and installing the insulation, and a preferred apparatus therefor, are disclosed.