A blind hem is a type of stitch that is done so that it prevents the fabric from unraveling, but isn’t visible from the “right” side of the fabric — the side you will be looking at. These hems are often used when you don’t want to be able to see a row of stitching on the finished product. For example, window hangings, skirts, and dressed are often hemmed along the bottom with a blind hem.
Certain fabrics may also require this type of hem. Some sheer or lightweight fabrics — for instance, organza and voile — tend to look better without heavy rows of stitching.
There are two types of blind hems: those that allow the fabric to stretch, and those that don’t. The simplest one is not used on stretchy fabric. This type of hem requires a pattern of three straight stitches and one zigzag stitch, repeated the entire length of the hem. The straight stitches only go through the backmost layers of the fabric, with only the high point of every zigzag going all the way through to the front layer of fabric. As a result, when you finish the hem and turn the fabric around, only the very top of each zigzag stitch will show.
The other type of blind hem is used on fabric that may need to be able to stretch. Because straight stitches won’t allow for any stretch, this type of stitch is a pattern of three small zigzags followed by one taller zigzag. When the hem is stretched, the zigzags will straighten out, allowing the fabric to stretch without breaking the thread and ruining the hem.
Blind hemming can be done either on a sewing machine or by hand. This particular stitch can be tricky to do on a sewing machine, since the seamstress needs to have very precise control over her machine. Some sewing machines offer only one type of blind hem — usually the kind that allows for stretch, since it can be used on almost any type of fabric — while others are programmed with both types.
In addition, sewing this type of hem with a sewing machine requires a special type of foot, known as a blind hem presser foot. The "foot" on a sewing machine is the little metal piece that sits underneath the needle and holds the fabric down as you sew. The presser foot is constructed with a special edge to guide your stitching and make sure the diagonal stitches go to the right place.
A blind hem can also be sewn by hand. Careful stitching will be required to ensure that the needle only picks up a tiny bit of the front layer of fabric every time. When done correctly, a hand-sewn blind stitch should be even more difficult to see than a machine-sewn blind stitch.