TWO rows of topstitching and why you should do it

If you are new to bra-making, you might wonder why the designer asks for two rows of topstitching, found on the side seam and the wire line. But why are two lines of topstitching needed…or warranted?

While it might look like a decorative choice, bra construction is actually closer to bridge engineering than standard clothing. Those two lines of topstitching are there because the wire line and the side seam are the highest-stress points of the entire garment.

Here is why one row of stitches just won’t cut it:

1. Creating a Channel

On the cup wire line, you aren’t just sewing two pieces of fabric together. You are also attaching a wire casing (called channeling, a soft, tube the wire slides into). The channeling is attached to the seam allowance around the wire line. But then we add two rows of topstitching. Huh?

• The First pass: the first line of topstitching is sewn close to the seamline to flatten the bulk as much as possible. It also keeps fabric that might form small pleats from doing so. The first line defines the wire line.
• The Second pass The second pass is on the outside curve of the channeling. Without two lines, the wire would have no incentive to sit flat against the body and would want to flip up and in! Just be sure to keep the two rows of topstitching apart enough to fit the width of the wire.

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2. Tension Distribution

Bras are designed to be worn under significant horizontal tension. The seams that take the brunt of the action are the side seams, so it makes sense to sew a reinforced seam.

• Preventing Seam Grinning: When you pull a bra band tight, a single line of stitching can stretch, making the threads visible (this is called “grinning”). Two lines of stitching distribute that pull across more fabric fibers, keeping the seam tight and invisible.
• Reinforcement: The side seam takes the brunt of the “tug-of-war” between the cups and the back band. Doubling the stitching ensures that if one thread snaps under pressure, the whole bra doesn’t come apart mid-wear.

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3. Creating a Flat Profile (Comfort)

Because bras are worn so close to the skin, internal seam allowances can be incredibly irritating.

• The Fell and Topstitch Method: In the side seams, the two lines of stitching are often used to “fell” the seam. This means the raw edges of the fabric are pushed to one side and stitched down flat. The most common use of felled seams is for jeans, but we can use them too.
• No Chafing: By stitching both sides of the seam flat against the band, you ensure there is no “flap” of fabric rubbing against your ribs throughout the day.

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4. Supporting the Side Stays

Some ready-to-wear bras have small plastic bones or stays in that side seam to prevent the band from rolling up or bunching. Just like the underwire, this stay needs a casing. The two lines of topstitching hold a pre-make casing to the seam, or by stitching two lines on the felled seam allowances, you can create a narrow pocket that holds the bone without having to buy or make casing. The bone is actually inside the two seam allowances.

Summary Table

Feature	Why Two Lines?	Benefit
Wire Line	Sews the channeling both sides	Holds the underwire in place.
Side Seam	Flattens seam allowances	Prevents skin irritation/chafing.
General	Distributes the stress on the stitches	Prevents the seam from “grinning” or snapping.

Here’s a video on that shows how I sew the topstitching and the channeling in a continuous line. and not have thread tails at both ends.