Glass insulation with an insolubilized asphalt binder

In a process for forming an acoustical or thermal insulating fibrous glass product comprising spraying a binder onto a downwardly flowing stream of glass fibers, collecting said sprayed fibers on a conveyor in the form of a blanket, and heating said blanket so as to bind the fibers with said binder, the improvement wherein said binder is a rubber-free, non-chemically modified asphalt emulsion and said heating comprises heating said asphalt for a sufficient period of time to bind said fibers and to convert said asphalt to a substantially insolubilized form, wherein said heating is done at a temperature of at least about 140.degree. C. for a period of time of at least about 50 hours.