A roll hem is necessary on very fine thin fabrics, so use a fine needle and fine thread or machine thread. Calculate 1 cm for the hem allowance. There are two methods. Either fold the edge under by 1 cm and insert the needle alternately into the fold edge and close to the hem allowance, catching in only 1 or 2 fabric threads each time. After several stitches, carefully pull the thread, thus rolling in the hem. Or roll up the hem allowance between thumb and fingers of one hand, while slip-stitching the little roll with the other.