Interlining is a cotton-type felt that is sandwiched between the front fabric and the lining. The main purpose of this barrier is to be a thermal insulator. The whole room will feel warmer in the winter, saving heat and money on energy bills. Interlining will also add weight to custom made curtains, giving them a lovely drape and weight when you hold them. The other notable difference an interlining can do is move the hem folds into an interior. Doing away with the stitching line to create a one-piece look.
Sateen Lining crease