Black Siri Interfacing Light Weight Hariform 100% Cotton 58" Pre-Shrinking All interfacings should be preshrunk. Sew-ins can be preshrunk through a press steaming process. Fusible can be preshrunk by immersing in a bowl of very hot (not boiling) water and allowing to sit until the water cools to room temperature. Gently squeeze, then roll in a towel to remove excess moisture and allow to air dry.