Flat-felled Seam
A flat-felled seam is a sewing specification that finishes by pressing the seam allowance to one side, enclosing it, and securing it with stitching from the right side so that the seam allowance edge does not show on the outside.
Contents6 sections
Definition and Overview
Flat-felled seam is a finishing method in which, after sewing two pieces of fabric together, one seam allowance encloses the raw edge of the other seam allowance and topstitching is applied from the right side. Because the seam allowance is enclosed inside, the wrong side is relatively neat as well.
The seam often appears as two parallel lines of stitching, and it is used as a specification that combines strength and design appeal. It is suitable for areas where fraying at the seam allowance edge should be prevented, such as side seams, underarm seams, yokes, and crotch seams.
Position in the Product Process
Flat-felled seam is carried out during the sewing process that assembles each part after cutting. It is characterized by requiring multiple steps: not only the initial seam but also trimming and folding the seam allowance, then applying topstitching.
In mass production, attachments or dedicated presser feet that match the specification may be used. On the pattern, it is important to specify the seam allowance width, the direction it will be folded, and the stitch position in advance, and share this with the production staff.
Procedure and Practical Points
In general, after the initial stitching, one seam allowance is trimmed to the required width. The remaining seam allowance is folded to enclose the trimmed edge, and it is secured by stitching near the edge. Depending on the fabric and specification, the order of operations may vary.
The folding direction is decided based on how it will look when worn, thickness caused by overlapping layers, and interference with other sewing processes. Keep the direction consistent for left and right products, and check the thickness in advance at areas where seam allowances concentrate, such as necklines and hems.
- In the specification sheet, state the flat-felled seam width and the number and position of stitches visible from the right side.
- Specify the color of the stitching thread, thread count, and stitch density from the viewpoints of both strength and appearance.
- During prototyping, check for seam shifting, wrinkling, and steps at curved sections and intersections of thick materials.
- For products that undergo washing or finishing, also check seam shrinkage and fading after processing.
Ordering and Quality Considerations
When placing an order, do not just specify "flat-felled seam"; also indicate which side it should be visible from, the folding direction, seam allowance width, and how the stitching should appear. Attaching sample photos or sewing samples helps reduce differences in interpretation between factories and personnel.
During inspection, confirm that the seam allowance edge is fully enclosed, that the stitching has not come off the seam allowance, and that the seam width and folding direction are consistent. Puckering is wave-like wrinkling caused by seam shrinkage, and attention is also needed to the combination of fabric, sewing thread, and thread tension.
Differences from Similar Terms
French seam is a finishing method that encloses the seam allowance like a pouch so the edge is not visible, but it differs from flat-felled seam in how the seam allowances overlap and in the structure of the stitching visible on the right side. For thin fabrics where you want to hide the seam allowance, French seam may be chosen.
Overlock is a finishing method that overcasts the seam allowance edge to prevent fraying. It does not enclose the seam allowance like flat-felled seam. Safety stitch is a method that combines a plain seam and edge finishing, and its process and appearance differ from flat-felled seam.
Frequently Asked Questions
What kinds of products use flat-felled seam?
It is often used for shirts, workwear, and denim products. It is suitable for areas where you want to keep the seam allowance edge inside, or where you want to show the two rows of topstitching on the right side as part of the design. However, depending on fabric thickness and stretch, another finishing method may be more suitable.
What information is needed when specifying flat-felled seam in a specification sheet?
State the folding direction, seam allowance width, number and position of stitches visible on the right side, and thread color. In addition, showing the stitch spacing, how curved areas are handled, and how overlapping thickness is treated in sewing samples or diagrams can reduce differences in interpretation of the finished product.
What quality problems are likely to occur with flat-felled seam?
Insufficient enclosure of the seam allowance edge, stitches coming off, variation in seam width, and puckering caused by seam shrinkage may occur. In particular, curved sections and thick materials are prone to shifting and steps, so it is important to conduct sewing tests with the actual fabric and check the product after washing before mass production.
