Costume designer Mark Bridges explained: “It was in the original material, the book by Matthew Quick. It really sums up that working-class world, and also [Cooper’s character’s] dedication to try to get back into shape to win his life back by any means necessary—even by looking ridiculous and causing complete humiliation to the whole family by running down the street like that.”
He also told, “The garbage bag was actually made so that it would be silent. We needed to wire the microphone on Bradley so that you would not hear the crinkle, crinkle, crinkle of a real garbage bag. It sort of had a silencer on it.” Asked how many garbage-bag costumes were made in total, Bridges tallied “five of six, just in case something happened. I have one in my garage, actually, just in case we need to do a reshoot or something.”
Source : vanityfair.com
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