An improved, fire-resistant, set gypsum composition contains set calcium sulfate dihydrate as the major ingredient and a reinforcing ingredient of resilient, flexible, boron-free glass fibers. Continuous filament forming glass compositions with a softening point preferably greater than about 1580.degree. F. (about 860.degree. C.) and more preferably greater than about 1681.degree. F. (about 916.degree. C.) may be used. The fibers typically are distributed as their separate constituent individual glass filaments uniformly throughout the set calcium sulfate dihydrate.