A flat-felled seam wraps one seam allowance around the other and topstitches it down, giving a flat, strong, fully enclosed seam. It is what jeans, work shirts and outdoor gear use.
The method.
One. Sew the seam with wrong sides together if you want the fell on the outside, right sides together if you want it inside. Jeans have it outside; shirts usually inside.
Two. Press both allowances to one side.
Three. Trim the under allowance to about half the width of the upper one.
Four. Fold the wider allowance over the trimmed one, turning the raw edge under, and press hard. A hot iron and firm pressure at this stage decide how flat the finished seam is.
Five. Topstitch close to the folded edge, through all layers.
Why it is worth the effort. It is the strongest common seam, it encloses both raw edges, it lies flat against the body, and it looks deliberate. On heavy fabric it is also more comfortable than a bulky pressed-open seam.
Practical points. Use a longer stitch, around 3 mm, for the topstitching. A jeans or topstitch needle and heavier thread if it is a feature. And clip nothing — the seam relies on being continuous.
The hard part is corners and junctions, where several felled seams meet. Plan the order of construction so you are never felling across a completed felled seam if you can avoid it.
A felling foot exists and folds the allowance automatically. It is worth having if you sew jeans regularly.
Questions people actually ask
Which side does the topstitching show on?
Whichever side you folded the allowance onto. Decide before you sew the first seam, because it determines whether you start right or wrong sides together.
My machine struggles at the seam junctions.
Four or more layers plus the fold is genuinely thick. Hammer the folds flat first, level the foot with a scrap, and turn the handwheel by hand.
Last reviewed 2026-08-11