Wendy Gardiner, Brand Ambassador for The McCall Pattern Company, shares her tips for flat fell and welt seams, perfect for denim, corduroy and bulky fleece fabric

A flat fell seam is a super strong, neat seam finish most often seen on jeans and reversible garments. A welt seam is very similar  both are great for heavyweight fabric. They are both relatively simple to sew but require remembering a slightly different construction order!


This method provides a lovely finish as the seam allowances are hidden away so both inside and outside of the garment look neat. It also means that the edges wont fray away. Often found on the outer legs of jeans, on mens shirts etc, it can also be used on unlined coats, jackets or any garment where the underside will show. It is best used on straight seams or those with a minimal curve.

To create this seam:

1. Sew the garment sections together with wrong sides together, adding the usual seam allowance. Press the seam to embed the stitches, then press seam allowance open.

2. Trim one seam allowance to 3mm. On the trousers this will usually be the back leg seam allowance so that thefront leg allowance wraps to the back.

3. Press the untrimmed seam allowance over the trimmed one, tucking under 3mm of the untrimmed edge, so neatly covering the narrow allowance at the same time.

4. On the RS, stitch close to the fold, through all the layers to secure.


This is another seam that is a good way to reduce bulk and hold seam allowances on heavyweight fabric flat.

On the outside of the garment, it looks like a top-stitched seam. On the inside, the seam allowances are neatly finished.

To create this seam:

1. Sew the seam with the right sides together as normal. Press the seam to embed the stitches. Press the seam allowances open.

2. Finish the seam allowance edge on one seam allowance with overcast, zigzag or by overlocking (without cutting off too much). Trim the other seam allowance to 3mm.

3. Press the neatened seam allowance over the trimmed one so they are both to one side and the narrow raw edge is covered by the neatened edge.

4. Working from the right side of the garment, top-stitch 1cm away and parallel to the original seamline, effectively holding the seam allowances in place on the underside as you sew.


This will look like a flat fell seam from the right side. Stitch as welt seam above but also sew another line of top stitching close to the seam line.

Practice this technique on our smart bag project. The download is completely free and will let you make a fun denim bag with flat fell seam details!

download free sewing pattern