How to Sew a Flat Felled Seam on a Sewing Machine

A flat felled seam is a strong, tidy seam finish in which the raw fabric edges are enclosed inside a second fold of fabric. You can see this finish on jeans, work shirts, pyjamas and many ready-to-wear garments. It creates a durable seam with no overlocker required.

This technique is especially useful when the inside of a garment will receive plenty of wear or when you want a polished finish on both sides. The stitching is visible from the outside, so neat spacing and consistent seam allowance matter.

Although it looks specialised, you can sew a flat felled seam on an ordinary domestic machine. The key is accurate cutting, careful pressing and choosing a fabric that can tolerate a little extra bulk.

Understand the seam structure

A flat felled seam begins as a standard seam with the fabric pieces placed right sides together. After the first line of stitching, one seam allowance is trimmed, while the other is folded over it. That wider allowance is then folded again to cover the raw edge and stitched down.

The finished seam has two parallel lines of stitching on the public side or inside, depending on the garment design. It is flatter and more secure than a simple pinked or zigzagged edge, though it does add a narrow ridge.

Use it for woven cotton, linen, denim, flannel, corduroy and lightweight wool. It is less suitable for very bulky coatings, loosely woven fabrics that fray excessively, or stretchy jersey. A mock flat felled seam can sometimes be adapted for knitwear, but a conventional overlocked finish is generally more flexible.

Prepare fabric and seam allowance

Check your pattern instructions before cutting. Some patterns include a seam allowance that suits a flat felled seam, while others require you to add extra width. A 1.5 cm allowance is workable, but 2 cm gives you more room to trim and fold accurately.

If you are still getting familiar with pattern markings, this guide to reading a pattern envelope can help you check fabric requirements, sizing and construction details before starting. Mark notches clearly, because the seam must be aligned before the enclosed finish is stitched.

Cut accurately and test the method on a fabric scrap. This is particularly worthwhile with denim or linen, where pressing behaviour and thickness can vary. Australian sewists may find that fabrics bought from Spotlight, Lincraft, local fabric shops or online indie retailers have different width and fibre content, so check the actual cloth rather than relying only on the pattern suggestion.

Sew the first seam

Place the fabric pieces right sides together and match the raw edges, notches and any stripes or checks. Pin across the seam or use clips if the fabric is thick. Sew at the chosen seam allowance with a straight stitch, backstitching at both ends.

Press the seam exactly as sewn first. This settles the stitches and helps prevent a ridge or twist. Then press both seam allowances to one side, usually towards the back of a shirt or towards the garment’s less visible area.

Trim one seam allowance to approximately 6 mm. Leave the other at its original width, usually 1.5 cm. Trim with sharp fabric scissors or a rotary cutter and ruler, keeping the cut parallel to the stitching. Remove loose threads before folding, as they can become trapped and make the finished seam lumpy.

Fold and stitch the enclosed edge

Open the longer seam allowance and fold its raw edge inwards by about 6 mm. Press along the entire seam before folding it over the trimmed allowance. A tailor’s ham, sleeve board or narrow pressing tool is helpful when working around curved sections.

Fold the pressed allowance over the trimmed one so the raw edge is completely enclosed. Press again and pin from the wider side. If the fabric is slippery, use plenty of pins placed at right angles to the seam, or hand-baste before machine stitching.

Sew close to the folded edge, keeping an even distance from the original seam. You can stitch from the garment’s inside or outside, depending on the design. Lengthen the stitch slightly for heavy denim, but test first so the seam remains secure without perforating the fabric.

Fabric or project	First seam allowance	Useful needle	Practical note
Cotton poplin	1.5 cm	Universal 80/12	Press carefully for a crisp finish
Linen shirt	1.5–2 cm	Universal 80/12	Trim frayed threads before enclosing
Lightweight denim	1.5–2 cm	Jeans 90/14	Use a hump jumper over thick layers
Flannel pyjamas	1.5 cm	Universal 80/12	Avoid excessive bulk at intersections
Cotton lawn	1.5 cm	Sharp 70/10 or 80/12	Make the second fold narrow and precise

Manage curves and bulky intersections

Flat felled seams are easiest on straight sections such as side seams, shirt yokes and trouser inseams. Curves need more patience because the outer edge travels a longer distance than the inner edge. Make tiny snips into the seam allowance where appropriate, taking care not to cut the stitching line.

At underarms, cuffs, waistbands and crossed seams, reduce bulk before folding. Grade the seam allowances in steps rather than cutting every layer to the same width. A wooden clapper can help hold a pressed fold flat after steam, while a hump jumper or folded scrap of fabric keeps the presser foot level over thick joins.

Avoid forcing the fabric under the machine. If the fold becomes distorted, stop with the needle down, lift the presser foot and reposition the work. Slow stitching produces a more professional result than trying to maintain speed through a bulky section.

Adapt the technique for different fabrics

Lightweight fabrics can be enclosed with a narrow finish, but very fine cloth may show every press mark. Use a lower temperature and a pressing cloth, especially with dark colours or delicate fibres. On linen, allow the fabric to cool before moving it so the fold sets properly.

Stretch fabrics require a different approach because a straight, rigid seam can restrict movement. If you are working with jersey, these neckband sewing tips explain how stabilisation, stretch and machine settings affect knit construction. A narrow zigzag, lightning stitch or overlocked seam is usually a better choice for areas that need to stretch.

For Australian weather, consider how the garment will be worn and washed. A heavy enclosed seam may feel warm in humid Brisbane summers, while it can be welcome in a durable overshirt for cooler Melbourne or Hobart conditions. Lightweight cottons and linen benefit from careful pressing, but they also need enough room for natural movement and laundering.

Keep the stitching neat

Use matching thread for a subtle finish or contrasting thread when you want the seam to become a design feature. Workwear-inspired garments often use gold or rust topstitching, while a pale thread on white cotton creates a clean minimalist effect.

Before sewing the final line, mark a guide with removable fabric chalk or place masking tape on the machine bed. Check that the seam remains the same distance from the fold. If your machine has an adjustable needle position, move the needle rather than steering the fabric aggressively.

These checks are especially useful for beginners:

• Sew a sample using the same fabric, thread and needle as the garment.
• Press every stage instead of trying to flatten the seam at the end.
• Trim only one allowance so the fold has enough width to cover the raw edge.
• Reduce bulk at crossings by grading and staggering the layers.
• Use a fresh needle when sewing denim, tightly woven cotton or several layers.
• Backstitch securely, then bury or trim thread tails neatly.
• Inspect the reverse side before moving to the next seam.

Finish, wash and evaluate

After the seam is stitched, inspect both sides for skipped stitches, puckering and exposed raw edges. If the fabric has shifted, unpick only the affected section, repress it and sew slowly over the repair. A flat felled seam should lie smooth without pulling the garment off grain.

Follow the fabric’s care instructions and prewash cloth before sewing whenever possible. This is important for cotton, linen and denim, which may shrink differently across the grain. In Australia, many home sewists rely on line drying in the sun, but strong sunlight can fade dark thread and fabric, so turn garments inside out where practical.

Care information is also worth recording for handmade gifts or small sewing businesses. Australia’s care-labelling standard AS/NZS 2621 is voluntary, but any care information supplied must be accurate and must not mislead consumers under Australian Consumer Law. A simple note such as “cold gentle wash, line dry in shade” can help preserve the garment and set realistic expectations.

Once mastered, this seam becomes a dependable alternative to an overlocker for shirts, trousers, jackets and children’s clothing. Its strength, clean appearance and enclosed edges make it especially valuable for garments that will be washed frequently or worn hard.