Some clothes just look better when they’re in motion. And what motion is more beautiful than that of a ballet dancer? Fashion designer Christian Siriano (of “Project Runway” fame) recently tapped three ABT Studio Company dancers to show off his Spring/Summer collection. Katerina Eng, Isabelle Seiler and Carolyn Lippert dance in this dreamy ad set in New York’s Waldorf Astoria Hotel. They look gorgeous—and so do the dresses.