An important part of nylon's popularity stems from DuPont's marketing strategy. DuPont promoted the fiber to increase demand before the product was available to the general market. Nylon's commercial announcement occurred on October 27, 1938, at the final session of the Herald Tribune's yearly "Forum on Current Problems", on the site of the approaching New York City world's fair.[17][2]:141 The "first man-made organic textile fiber" which was derived from "coal, water and air" and promised to be "as strong as steel, as fine as the spider's web" was received enthusiastically by the audience, many of them middle-class women, and made the headlines of most newspapers.[18]:141 Nylon was introduced as part of "The world of tomorrow" at the 1939 New York World's Fair[24] and was featured at DuPont's "Wonder World of Chemistry" at the Golden Gate International Exposition in San Francisco in 1939.[17][25] Actual nylon stockings were not shipped to selected stores in the national market until May 15, 1940.