Worlds Fairs are now so passé that The Simpsons once spent a whole episode relentlessly mocking the 1982 fair in Knoxville; the U.S. withdrew a decade ago from the international organization that mounts them. But during the troubled decade of the 1930s, a series of six fairs in the U.S.—-culminating in the storied 1939 Trylon-and-Perisphere fair in Queens—-offered downbeat Americans a shining beacon of futurism. In “Designing Tomorrow,” the National Building Museum mulls the fairs’ societal impact.

To be honest, the fairs’ legacy is a mixed bag. The upside includes a whole bunch of art deco design (the bold posters, sprawling realist murals, and classical-moderne architectural flourishes have all aged tremendously well) as well as some lower-profile advances, such as the fine-tuning of how to direct visitors efficiently through crowded attractions. But the downside is apparent as well—-relentless corporate sponsorship (with its affiliated cheesy architecture, public-relations spin, and overbearing branding) as well as a series of questionable “advances” touted at the fairs, such as the use of asbestos as a building material and a push to shape landscapes roughly for the benefit of the automobile. Ultimately, it’s apt that most of the fair sites were razed shortly after the attractions closed, leaving our more cynical generation with little but tacky souvenirs and heroic posters to remind us of what the fuss was all about.

Through July 10 at the National Building Museum, 401 F St. NW. (202) 272-2448. On view 10 a.m to 5 p.m. Monday to Saturday and 11 a.m to 5 p.m. Sunday.