Theory Perfect Sheath Dress in Black. - size 0 (also in 2,6) Theory Perfect Sheath Dress in Black. - size 0 (also in 2,6) Self: 88% nylon 12% elastaneZipper Binding: 94% poly 6% polyurethane. Dry clean only. Partially lined. Double strap detail. Hidden back zipper closure. THEO-WD371. I0107604. Theory is a visionary concept for modern intelligent fashion forward people. Founded in New York and made by the finest of fabrics, this makes the working everyday person feel powerful, ready to face their day.