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Atonement

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''With Cecilia Tallis' clothing, we wanted everything to be as light as possible, so that she was this beautiful butterfly wilting in the heat,'' says Atonement costume designer Jacqueline Durran, referring to Knightley's character. The barely-there garments were particularly important for a sequence that takes place on a summer evening in 1935, when Cecilia and her childhood pal-turned-paramour (McAvoy) make love against a bookcase in the Tallis family library. For this key scene, Durran created a gown of featherweight silk satin, custom-dyed emerald. Since the Ian McEwan novel on which the film is based treats the frock as a character unto itself, partly responsible for igniting the couple's passion, Durran felt it was crucial that ''instead of being constructed around Keira's body, the dress skimmed her [frame] and added to a feeling of semi-nakedness.''

Director Joe Wright worked closely with Durran, who earned an Oscar nod for their previous collaboration, 2005's Pride & Prejudice. He drew on lessons his puppeteer mother had taught him about the importance of a garment's movement. ''I always had this idea that when Keira lifted her knee up, the dress would just fall away,'' he says, before adding with a laugh: ''Making a dress that works while having sex standing up —it's a bit tricky.''

Even tougher was designing a period-appropriate (read: modest) swimsuit that wouldn't appear ''stuffy and old-fashioned to the modern eye,'' says Durran. She found inspiration in French photographer Jacques-Henri Lartigue's ''decadent, rich, and lush'' shots of 1920s and '30s south-of-France bathing beauties. But unlike the stodgy wool swimsuits from the era, Knightley's was made of a far more practical stretchy synthetic. And the white rubber cap? ''You'd have to be as beautiful as Keira to look that great in it. Lots of people can pull off swimsuits, but pulling off that hat is amazing.''