For years I struggled to get a professional finish on shirt-tail hems - until I found my sewing bestie, Steam-A-Seam.
In sewing there are many ways to complete the same task. One of my joys as a sewist is finding the method that works best for me. I'm always searching for the method that gives the best result with the simplest procedure - this technique does exactly that.
Steam-A-Seam (SAS) is a strip of paper backed, double-sided, fusible web used to fuse (glue) two layers of fabric together. I often use SAS in my sewing practice as a quick and easy form of "basting." In this technique, SAS allows you to manipulate the hem edge around the paper backing for a crisp, uniform, curved hem. You will form the shape first, fuse it into place, and then sew it down.
For shirt hems I use the 1/4" width. Press SAS along the edge of the hem. The strip is straight, but will form around the curve. Try to follow your edge as close as possible to keep the shape. Don't try to lay the tape down the entire length of the hem at first, press it little by little. It will make forming it around the curve easier. DO NOT REMOVE THE PAPER BACKING.
Leave the paper backing on. It will give a nice stiff edge to press against as your fold the hem into place. Begin by folding 1/4" up, press against the edge of the paper tape to form a crisp fold. It may buckle a little but will be fine in the end. Repeat and press up the next 1/4", giving you the finished double fold hem placement.
Once you have folded and pressed your hem into place, you may open the folds back up and remove the paper backing. The tape will be slightly tacky and will hold in place while you fold the hem back into place. Press once again.
TIP: Sometimes the paper backing does not want to separate from the fusible tape. Try re-heating the SAS with your iron, use a pin to help separate the tape from the backing, and, once loose, peel the paper backing off at an angle.
All that's left to do is sew your hem in place. You will not need pins since your hem is now fused into place. Fusing the hem also allows you to sew from the top side of the work, maintaining nice, even topstitching.