Understitching is an understated and often overlooked technique, but one every dressmaker should consider. It is often found in pattern instructions for neckline facings and sleeve facings and is a method for folding facings flat. Try these simple steps to learn how to understitch and see how easy it really is.
Why Understitch?
Understitching just gives a facing that really professional finish and prevents the facing from rolling over to the front of the garment.
The advantage of using this technique is that you can hold the facing in place while keeping a clean and unstitched look around the outside of the neckline or armholes.
Understitching will also give a top-class finish to duvet covers and frilled edges or other projects that require a turned edge to sit flat.
Another common place understitching is found is in waistband edges especially in lined skirts.
How to Understitch
Supplies
General Supplies: All you will need is your regular sewing tools – pins, iron and your garment. (Further reading: Beginner sewing kit)
Understitching Foot: Understitching is sewn with an all-purpose sewing foot so you don’t need any specialty foot.
Understitching Thread: If your facing is a contrast color, match the thread to the facing rather than the outside fabric. The row of understitching won’t show on the outside of the garment.
In my samples, I used a cream thread which almost invisibly blended into the orange patterned fabric I used for the facing.
Step One: Prepare the Facing
Prepare and stitch the facings as usual. I have a full tutorial on how to sew facings and stay stitching facings but the basic steps to add facing to a neckline are –
- If necessary, stay stitch the edges of the facings and neck. Since the neck is cut on the bias it can stretch out of shape as it is being handled in the sewing process. Stay stitching prevents the neck from stretching and wrinkling.
- Sew the facing front and back at the shoulders with right sides together.
- Sew the garment front and back at the shoulders with right sides together.
- Press open all shoulder seams.
- Place the facing over the neck with right sides together, matching the shoulders and stitch around the neckline.
- Clip all the curves of the neckline.
- Press the facing away from the neck at the seam. The clipping should release most of the tension allowing you to press the seam flat. It may look and feel a bit bunchy but the area to understitch will be pressed and ready to sew neatly. When you press the facing open. the seam allowance should be underneath the facing and not the garment.
Extra Preparation Tips:
If your seam allowance is really thick and bulky, it may be necessary to grade your seam. This means cutting back the seam allowance in layers to reduce bulk. If you are using a cotton fabric this will not be necessary.
Further Reading: How to sew facings
Sew Shoulders 
Press Open Seams 
Sew neck 
Open Facing
Step Two: Understitching the Facing
With your facing open and separate from the main part of the garment, machine stitch the facing on the right side, following the curved edge.
Keep the machine stitches close to the edge but on the facing at all times.
Extra Understitching Tips
- You will be stitching through the facing and catching in the seam allowance underneath.
- The row of understitching will be approximately 1/8 inch (3mm) from the seam on the facing side.
- Try a stitch length of 2.0. Smaller stitches tend to look neater and hold the facing in place better.
Step Three: Press the Understitched Facing
Press the finished facing inside the garment and see how beautifully flat the neckline sits with the understitched edge.
The understitching will allow the facing to roll very slightly to the inside so that it is not visible from the outside.
Understitching will prevent any rolling edges and the facing will lie flat and well behaved. A really smart and professional finish.
Alternative – Bias Tape vs Understitching
If you are looking for an alternative to understitching then consider bias tape. Bias tape is an alternative way to finish necklines and armholes and also gives a really clean finish.
You can use it for a bias v-neck or a bias round neck.
If you look closely at the round neck photo below, you will see that a row of stitching approximately 1/2 inch (12mm) from the edge of the neck is visible. This is the main difference between using bias tape for necklines and understitching.
Understitching is invisible on the outside of a finished garment, while bias tape will result in a row of stitching. Which finish is best is just personal preference and will often depend on the fabric you are using.
Bias V-Neck 
Bias Round Neck
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