Oct 30, 2026
Activewear Stitch Types Explained: Flatlock, Coverstitch and Bar-Tack
Four-needle six-thread flatlock, three-needle five-thread, coverstitch, bar-tack and bonded seams explained, with where each construction belongs on a legging.
Two leggings can use the same fabric, the same pattern and the same factory, and still feel completely different on the body. The difference is often the stitch. A four-needle six-thread flatlock lies flat and moves with the fabric. A four-thread overlock leaves a raised ridge that you feel against the skin after twenty minutes. Both are correct engineering. They are simply correct for different places on the garment.
This is a working glossary of the constructions we use on activewear, written for buyers who have to read a sample room's comments and decide whether they agree. The numbers below are typical shop-floor ranges for 150 to 260 gsm stretch knit. Confirm them against your own fabric before you write them into a tech pack.
Why stitch choice is a specification, not a preference
A seam has to do three things at once. It has to hold under tension, it has to stretch with the fabric without cracking, and it has to feel acceptable against skin. No single construction wins on all three, so the garment is built from a mix: flat seams where the body moves most, stronger raised seams where the load is highest, coverstitch where an edge needs to stay flat, and bar-tacks where a point will be pulled.
When a buyer writes "four-needle six-thread" across every seam, the factory will either comply and charge for the extra operations, or quietly substitute where it thinks nobody will notice. Naming the stitch per panel removes both outcomes.
The five constructions you will see on a legging
Four-needle six-thread flatlock
This is the workhorse of performance leggings. Four needle threads pass through the fabric and two looper threads form the underside, so the seam is joined and covered in one operation and both faces stay flat. The face looks like two parallel rows of parallel stitching. The back looks like a dense net.
Where it belongs: side seams, inseams, the seat seam, and any seam that sits against the body during movement.
Typical settings: 3 to 4 mm stitch width, 12 to 14 stitches per inch, differential feed set slightly gathering on soft fabric. The seam can be trimmed single or double, which changes the exposed edge and matters on prints.
What it cannot do: it is not the strongest seam for a high-load point, and it does not like very thick stacks. If a panel join includes a waistband, a pocket and a lining, the flatlock will struggle and the seam will ripple.
Three-needle five-thread
Three needle threads and two looper threads. The result is a flatter than overlock but slightly raised seam, stronger than a flatlock in the direction of the seam line. It is common on activewear where the seam is expected to take load rather than lie against skin.
Where it belongs: waistband attachment on heavier styles, outer leg seams on compression garments, panel joins on thicker fabric.
Typical settings: 4 to 6 mm width, 11 to 13 stitches per inch, with the looper tension set so the seam does not cup.
Four-thread overlock
Two needle threads and two looper threads, with the raw edge enclosed in a net. It is fast, strong and cheap to run. The downside is the ridge: the seam stands up from the fabric and can be felt against the skin.
Where it belongs: inside seams that will not touch skin, secondary construction, and linings. On an unlined legging it is usually the wrong choice for a centre front or an inner thigh.
Typical settings: 4 to 6 mm width, 10 to 12 stitches per inch, differential feed set to prevent the seam from waving.
Coverstitch
Two or three needle threads with a looper that covers both faces. The face shows parallel rows of straight stitching. The back shows a flat net. It stretches well and it is the standard finish for hems and for joining a folded waistband.
Where it belongs: leg openings, sleeve hems, waistband top edges, and anywhere a raw edge must be folded and held flat.
Typical settings: 6 mm folder, 12 to 14 stitches per inch, with the looper tension balanced so the fold does not tunnel.
What to watch: tunnelling, where the fabric between the needle rows lifts. It appears when the looper tension is too high or the folder is too wide for the fabric weight.
Single-needle lockstitch
The ordinary straight stitch. It does not stretch, which is why it is used sparingly on knit activewear, but it is still the correct choice for zippers, bar-tacks, labels and any place where a fixed, strong line is needed.
Where it belongs: the zip placket, the fly topstitch, woven labels, and bar-tack reinforcement.
Typical settings: 10 to 12 stitches per inch, with a stitch length short enough to hold but long enough not to perforate the fabric.
Bar-tacks: the smallest detail that shows the most
A bar-tack is a short, dense zigzag or box of stitches placed at a point that will be pulled. On leggings it appears at the base of the fly, at the corner of a pocket opening, and at the ends of a waistband join.
The specification matters more than buyers expect. A bar-tack that is too short will tear out. One that is too dense will perforate the fabric and create a hole along the stitch line. A typical working range is 12 to 16 mm long and 42 to 56 stitches, in a thread matched to the seam.
Placement matters just as much. A bar-tack that lands on top of a seam allowance stack creates a hard lump that presses into the body. Move it 3 to 5 mm and the same bar-tack becomes invisible.
Bonded seams: when glue replaces thread
On high-end waistbands and hems, a polyurethane tape is applied with heat and pressure instead of stitching. The result is genuinely flat and there is no needle hole, so printed and fine gauge fabric look cleaner.
Bonding has its own failure modes. It needs a clean, dry surface. It needs the right temperature, pressure and dwell time for the specific tape and fabric. It does not tolerate contamination from softeners or finishing agents, and it cannot be re-worked the way a seam can. On a garment that will be washed hot or tumble dried, a bonded seam can lift at the edge long before a stitched seam would fail.
Ask for a wash test on the bonded sample, not just a visual check. Three cycles at 30 degrees and a look at the edge will tell you more than any lab report about the process window.
Needle and thread: the two consumables that decide seam life
Needle. Use a round point or light ballpoint needle. A sharp point cuts the knit loops and creates a run. Size follows fabric weight: 70/10 or 75/11 for 150 to 220 gsm, 80/12 for 240 gsm and above. On printed fabric, always test the smaller needle first.
Thread. Use a corespun polyester with high elongation and a soft, bulky hand. A rigid thread on a stretch seam will pull the seam line tight, and the fabric will ripple around it. Match the thread's elongation to the fabric's, not to the colour card.
Thread consumption. Needle threads pass through the fabric on every stitch, so they are consumed faster per stitch than looper threads, which form loops along the edge. In a three-needle five-thread seam there are three needle threads and two looper threads. In a four-needle six-thread seam there are four needle threads and two looper threads. When a factory quotes thread consumption, ask which ratio it used, because the needle-to-looper split changes the number significantly.
Reading a stitch spec: what the numbers mean
Three-needle five-thread means three needle threads plus two looper threads. The first number counts needles, the second counts all threads.
Four-needle six-thread means four needle threads plus two looper threads, for six in total.
Double-needle in a coverstitch context means two needle threads plus two looper threads, four in total.
Stitches per inch describes density along the seam. Higher is not better. Too dense perforates fine fabric and stiffens the seam. Too sparse leaves the seam open under stretch.
Stitch width describes how far the needle rows sit from the seam centre. Wider spreads the load and looks more technical. Narrower looks cleaner and is easier to keep flat.
A short glossary of legging pattern terms
Waistband. The band at the top, usually cut on the cross grain and joined to the body with a three-needle five-thread or coverstitch seam.
Front panel. The front leg piece. On a no-front-seam legging, the left and right fronts are cut as one piece to remove the centre seam.
Back panel. The rear leg piece, shaped to follow the seat curve.
Back yoke. A separate piece across the seat, used to shape the rise or to place a seam where it lifts rather than flattens.
Gusset. The diamond or triangle insert at the crotch. It removes the four-way seam junction and reduces friction. A gusset is a fit decision, not a decoration.
Side seam. The seam from waistband to hem along the outside of the leg.
Inseam. The seam along the inside of the leg, from gusset to hem.
Rise. The distance from the crotch point to the waistband, measured at the front and at the back. Front rise and back rise are different numbers and should be specified separately.
Crotch depth. The vertical distance from the waist line to the crotch line on the pattern. It decides how the garment sits, not how it looks on a hanger.
Hip line, thigh line, knee line. Horizontal reference lines on the pattern used for grading and for measuring. If a measurement is specified at the thigh, it should say where the thigh line sits.
Leg opening. The finished circumference at the hem, measured flat and doubled, or measured around depending on the buyer's convention. State the convention.
How we specify stitches by panel
Waistband join: three-needle five-thread or coverstitch, depending on whether the band is folded or attached.
Side seam and inseam: four-needle six-thread flatlock, single cut on prints, double cut on solids.
Gusset: four-needle six-thread flatlock with a narrow allowance, plus a bar-tack at each end.
Hem: coverstitch with a 20 to 25 mm fold, or bonded tape on premium styles.
Fly and zip: single-needle lockstitch with a bar-tack at the base.
Cup edge on a built-in bra: dense overlock, so the edge stays flat and does not roll after washing. This is the detail most buyers do not specify and most wearers feel first.
Mistakes we see buyers make
Specifying one stitch everywhere. It either overbuilds the garment or leaves the wrong seam in the wrong place.
Judging a seam on a hanger. Every seam looks flat when the garment hangs. Judge it on a body, in motion, after ten minutes.
Ignoring the inside. A seam that photographs well and feels rough against the skin will generate returns for a different reason than fit.
Changing thread to match the colour card. Thread is chosen for elongation and strength first, colour second. A perfect colour match on the wrong thread is a seam failure waiting for the first wash.
Approving a bonded seam without a wash test. Bonding is a process, not a material. The process window is narrow and it does not forgive a bad sample.
Questions buyers ask us about stitches
Is four-needle six-thread always better than overlock?
It is flatter and more comfortable against skin, and it costs more to run. On a seam that never touches the body, overlock is the correct engineering choice and the money is better spent elsewhere.
Why does my sample have a raised ridge on the side seam?
The seam was probably built with a four-thread overlock instead of a flatlock. Ask for a photo of the inside face, then compare it with the spec.
Can we mix stitch types in one style?
You should. Most leggings use three or four different constructions. A single-stitch specification is usually a sign that nobody wrote a real one.
Does stitch density affect stretch?
Yes. Very dense stitching reduces the seam's ability to extend and can cause the fabric beside the seam to take all the strain. Twelve to fourteen stitches per inch is a practical balance for most stretch knits.
How do we check seam quality at inspection?
Pull the seam to 30 percent extension, release, and look for waviness and grin-through. Then check the inside face for loose loops, skipped stitches and thread tails. A visual check alone misses most of it.
The bottom line
Stitch construction is where comfort, durability and cost meet. A legging with the right seam in the right place feels like nothing on the body. The same fabric with the wrong seam feels like a garment you want to take off. Specify it panel by panel, and ask for the inside face in every approval photo.
If you are building a legging, short, bra or zip-front top and want a second opinion on the construction, send us the tech pack or a photo of the inside seam. Email breezsportswear@126.com or message WhatsApp +86 181 4865 3131. Breez Sportswear builds private-label activewear and will tell you which construction fits the fabric you have chosen, before the sample budget is spent.
Related reading: seamless versus cut and sew, from tech pack to bulk production, and developing private-label leggings.
Styles that depend on this construction: no-front-seam leggings, built-in-cup sports bras, and 2-in-1 yoga tops. To discuss a construction, use the contact page or send a photo of your inside seam.