Seams: parts, types and functions

1Why this matters

Every garment you wear is held together by seams: the side seams of your school shirt, the shoulder seams of a jumper, the double-stitched inside-leg seams of a pair of jeans. When a tailor at Kimironko market turns a length of kitenge into a dress, most of the work, and most of what decides whether the dress lasts, is in the seams.

In this lesson you will learn the parts of a seam, what seams are for, the main types, and the qualities of a good seam. The next three lessons teach you to make the three key seams step by step.

2What a seam is

A seam is the join where two or more layers of fabric are held together with stitches. Before the sewing machine was invented every seam was sewn by hand; today seams are sewn by hand, by machine, or both.

3The parts of a seam

• Right side (RS): the side of the fabric meant to be seen, usually brighter or with the clearer pattern. Wrong side (WS): the inside.
• Raw edge: the cut edge of the fabric. On most woven fabrics it frays (loose threads pull away).
• Stitching line (or fitting line): the line along which the seam is sewn.
• Seam allowance: the strip of fabric between the stitching line and the raw edge. Home-sewing patterns usually allow 1.5 cm.
• Notches (balance marks): small marks on the edges that are matched so the pieces line up.
• Selvedge: the firm, woven edge along each side of a length of cloth; it does not fray.

4Functions of seams

1. To join pieces of fabric into a garment or article.
2. To shape the garment so that it fits the curves of the body; for example, side seams and seams from the shoulder to the waist.
3. To strengthen places that take strain, such as the inside legs of trousers.
4. To neaten and enclose raw edges so they do not fray in the wash.
5. To decorate, for example with a row of top-stitching in a contrasting thread, or piping inserted into the seam.

5Types of seams

Seams are also named by their position: side seam, shoulder seam, centre back seam, inside-leg seam (inseam).

6Stitches used when making seams

• Tacking (basting): long, temporary hand stitches, about 1 cm long, which hold the pieces in place before machining. They are removed afterwards.
• Running stitch: small, even stitches in and out of the fabric; quick but not very strong.
• Backstitch: each stitch goes back to meet the one before, making a strong continuous line. It is the hand stitch for a permanent seam when there is no machine.
• Machine straight stitch for the seam itself, and overcasting or zigzag to neaten raw edges.

7Qualities of a good seam

• An even width all along, following the stitching line.
• Straight, or smoothly curved on a curved edge.
• Flat and well pressed, with no puckers.
• Secure at both ends.
• Raw edges neatened or enclosed.
• Suited to the fabric and to how the article will be used and washed.

Worked example: cutting out with a seam allowance

Uwase is making a square cushion cover that must measure 40 cm by 40 cm when finished. The pattern uses a 1.5 cm seam allowance. What size must she cut each of the two squares?

Step 1 The finished size is measured between the stitching lines.

Step 2 Each side of the square needs an allowance at both edges: 1.5 cm + 1.5 cm = 3 cm.

Step 3 Cutting size = 40 cm + 3 cm = 43 cm by 43 cm.

A common mistake is to add only one allowance (41.5 cm), which makes the finished cover 1.5 cm too small.

Practice

Solution. The stitching line is where the seam is sewn; the raw edge is the cut edge of the fabric. The strip between them is the seam allowance.

Solution. 50 + 1.5 + 1.5 = 53 cm.

Solution. They hold the layers firmly in place, so the fabric cannot slip while it is machined, and they are easier to sew around than pins. They are temporary and are pulled out once the seam is sewn.

Solution. It joins the front and back leg pieces, and it strengthens the leg at a place that takes a lot of strain and rubbing. (It also neatens the raw edges, which are enclosed.)