Fashion designers like Issey Miyake, Rei Kawakubo and Ronaldus Shamask have made clothes from Junichi Arai's fabrics. Interior designers have turned his fabric into canopies. But for Mr. Arai, 58 years old, textiles are not just functional materials but also a medium for art. Mr. Arai, Japan's pre-eminent textile designer, has woven silk to look like a gossamer spider's web and, using computer-aided technology, has woven wool and nylon to make fabric with squares on one side and triangles on the other.
''It used to be that the finest fabric was silk,'' Mr. Arai said, ''but natural fibers will be changed by technology.'' He is working with a nylon-coated polyester that can be made into raincoats weighing less than four ounces. His fabrics, $25 to $125 a yard, are sold through decorators in the Ilana Goor showroom, the Designers & Decorators Building, 979 Third Avenue at 60th Street.