In Engi-shiki (old documents, 927 AD) oiled clothes are noted to have been used as rain covers of outdoor furniture and moisture-proof packages for drugs. There are also descriptions about raw materials for making oiled silk clothes. The author interprets the process of making oiled clothes as follows: (1) Raw perilla oil is pre-polymerized by long time heating in kettles with woodfire. (2) This pretreated oil is spread on silk cloth. (3) The oil on the silk cloth is exposed to air; the oil, absorbing oxygen from the air, changes from liquid to solid flexible film. (4) This phenomenon is the oxy-polymerization of unsaturated fatty oils; the resulting solid flexible film being named Linoxyn in modern chemistry. (5) The resulting oiled silk cloth in those days may be comparable to the oiled paper of Japanese lanterns and umbrellas of the present day.