The invisible seam sneak stitch is by far the prettiest way to sew an opening in a sewing project.
It is used when sewing something that should be completely closed and e.g. filled with wadding. Examples of products where this technology works perfectly are baby nests, soft toys or why not soft balls.
The seam is usually done last of all, after you have sewn all the parts together right sides together, turned the fabric right sides out, filled with wadding and only have a small opening left that needs to be sewn together.
The seam is pre-stitched, but don't let that put you off! It's a very simple stitch once you understand how it works.
Below you can see a video where I show how to sew a stealth stitch step by step. Keep in mind that I use a thick cotton thread and a large needle to show what I'm doing better, you should preferably use regular sewing thread (eg the same one you used in the sewing machine to sew the rest of the project) and a thin sewing needle .
Tips for best results
Press the seam allowances firmly so that you have a sharp folded edge to follow as you sew. Then the seam will be straight and follow your machine-sewn seams perfectly.
Try to make stitches of even length
If your sewing thread is very thin and easily comes off when you tighten the seam, you can try having it double or use a slightly thicker and more durable sewing thread.