The flat-fell seam

1Why this matters

Turn a pair of jeans inside out and look at the inside leg seam. It is flat, it has two parallel rows of stitching, and you cannot find a raw edge anywhere. That is a flat-fell seam. It is the strongest of the common seams, which is why it is used on clothes that are worn hard and washed often: jeans, work overalls, sportswear, school shorts and strong bags.

In this lesson you will learn why the flat-fell seam is so strong and how to make one.

2What a flat-fell seam is

In a flat-fell seam one seam allowance is trimmed narrow, and the other is folded over it, with its raw edge turned under, and stitched flat to the garment. The folded part is called the fell. The seam has two rows of stitching, both visible on the right side.

Why it is strong and useful:

• two rows of stitching share the strain;
• the layers are locked together, so the seam cannot pull apart;
• no raw edges are left, so it cannot fray, however often it is washed;
• it lies flat, so it is comfortable, and it looks neat on both sides, so it suits reversible articles.

In factories, jeans seams are made in one pass on a special machine with two needles. At home the same result is built up in steps.

3Making a flat-fell seam, step by step

These steps put the fell on the right side, as on jeans.

1. Place the pieces with their wrong sides together. Pin, tack and stitch 1.5 cm from the edge (row 1). Remove the tacking.
2. Press both allowances to one side. Trim the lower allowance to about 5 mm; leave the upper one at full width.
3. Fold the raw edge of the wide allowance under by about 5 mm, so that it wraps over the trimmed allowance.
4. Press the folded allowance down flat onto the garment and pin it, with the pins at right angles to the seam.
5. Edge-stitch (row 2) close to the fold, about 2 mm from it, through all the layers.
6. Press. Check that row 2 is straight and parallel to row 1, and that no raw edge shows anywhere.

If you start with the right sides together instead, the fell ends up on the inside of the garment. This version is often used on shirts, where a smoother outside is wanted. It still shows two rows of stitching on the right side.

Worked example: comparing the fell and the seam allowance

(b) How wide is the finished fell? The upper allowance is 15 mm wide; turning 5 mm of it under leaves 15 − 5 = 10 mm, which covers the 5 mm trimmed allowance with room to spare.

(c) Why is this seam better for the bag than a plain seam with pinked edges? A bag carrying heavy vegetables strains its seams, and pinked cotton edges fray. The flat-fell seam has two rows of stitching and no raw edges, so it is stronger and will survive washing.

Practice

Solution. Two: the first seam line and the edge-stitching close to the fold.

Solution. So that the wide allowance can fold right over it and enclose it. It also reduces bulk, so the seam lies flat.

Solution. For example jeans, work overalls and sports shorts (also shirts and bags). They are all worn or used hard and washed often, so they need a strong, flat seam with no raw edges.

Solution. The stitching may miss the trimmed allowance or catch the folded edge unevenly, leaving the fell loose so that it can lift or let the raw edge escape. Row 2 must run close to the fold, through all the layers.