A side slit stays closed when four things are specified together: a real bar-tack across the slit top, a slit depth that matches the stride the garment needs, a small reinforcement behind the slit top in loose or slippery fabric, and a seam test after washing. Specify only one of these, and the kaftan or skirt slit can still split or gape.
This guide covers side slits and hem slits on kaftans, skirts and dresses. It does not cover neck slits.
Where does the load go at the top of a skirt or kaftan slit?
The load goes to the last few stitches of the side seam, right at the top of the slit. Below that point, the front and back panels of the skirt or kaftan hang free. Above that point, the side seam holds them together. When the wearer walks, sits or climbs a step, the two slit edges move apart. All of that spreading force arrives at one small point, where the seam ends.
The wearer needs that movement. A sample-maker at Megan Nielsen made a silk crepe de chine midi slip dress with no slits, and after three years of wear the team concluded that at least one slit is needed to walk comfortably. So the slit cannot simply be closed. The slit top has to be built to take the force.
Two things decide how much force reaches the slit top in a dress or kaftan:
- Hem width. A narrow hem in a straight skirt leaves the legs little room, so the slit opens wider with each step.
- Slit depth. A short slit in a narrow skirt is forced open on every stride. A deeper slit opens with less force.
Why does the top of a skirt or kaftan slit split, and what must a bar-tack hold?
The slit top splits because the end of the side seam carries the whole spreading load on a few stitches, and in loose fabric the yarns slide out from under those stitches. There are two different failures here, and the spec should name both.
Failure 1: the thread unravels. A seam that ends with only a short back-tack can open stitch by stitch. A bar-tack stops this. A bar-tack is a dense block of zigzag stitches across the stress point. Sewing guides list side slits among the standard bar-tack locations. One pattern company instructs a bar-tack about 2.5 cm long at the top of each side slit. The American & Efird stitch guide prefers ISO stitch type 304, a zigzag lockstitch, for bar-tacks where stitch security matters, and says a bar-tack spec should state the length and width of the tack. One industry stitch matrix lists a 304 bar-tack at about 6 to 19 mm long, about 3 to 4 mm wide, with around 28 stitches per cycle. That matrix is for denim, so treat the figures as a reference, not a rule for a viscose kaftan.
Failure 2: the fabric slips. The thread holds, but the yarns of the fabric slide apart and leave a hole beside the bar-tack. This is seam slippage. The thread maker Amann says the root cause usually lies in the fabric itself, not in the seam or the thread. Loose weaves and smooth, slippery yarns give stitches little to grip. A bar-tack alone cannot fix this. In loose viscose, rayon or silk-like polyester, a dense bar-tack can even cut a line of perforations that tears. That is why the slit top in these fabrics also needs a small patch of interfacing behind it (see the table below).
Wet strength matters for viscose skirts and kaftans. A University of Glasgow study found that some viscose fabrics lost up to 50% of their strength when wet. A slit top that holds in the dry sample can fail during washing, when the fabric is weakest and the garment is twisted in the drum.
For the seam itself, a bar-tack only works if the seam it closes is sound. Amann recommends, for critical seams, a seam allowance of at least 1 cm and at least 4 stitches per cm. Our guide to why seams fail: thread, needle and stitch covers those choices in more detail.
Reinforcement options at the slit top
| Option | What it does | Works best in | Limit |
|---|---|---|---|
| Back-tack only | Locks the thread end of the side seam | Firm cotton, short decorative slits | No protection against fabric slippage or tearing |
| Bar-tack (stitch type 304) | Spreads the load across a dense block of stitches | Cotton poplin, cotton voile, linen | In loose or slippery fabric, can perforate the cloth and tear beside the tack |
| Fused interfacing patch + bar-tack | Holds the yarns in place so the bar-tack has something to grip | Viscose, rayon crepe, georgette, satin | Patch can show through very sheer fabric; needs a matched weight |
| Fusible edge tape along the slit edges | Stops the slit edges stretching and rolling open | Bias-cut panels, drapey viscose kaftans | Adds a firm line; wrong tape weight makes the edge stiff |
| Wider slit facing, topstitched | Gives the slit edge weight and a clean fold | Skirts and dresses in medium-weight fabric | Uses more fabric; bulk at the hem corner unless mitred |
Interfacing makers sell tape for this job. Vlieseline describes its Edgefix tape as made for plackets, cuffs, slits and pockets.
Why does a skirt or kaftan slit gape or ride up? Hem weight, drape and seam allowance
A slit gapes or rides up when the fabric around the slit stretches, the hem pulls the edges apart, or the slit edges are too narrow to lie flat. These are three separate causes in the fabric and the pattern.
Hem weight. A heavy hem pulls down on the panels on each side of the slit. On a kaftan with tassels or pom-pom trim, the trim adds weight at the hem. In a drapey fabric, the panels stretch under that weight, and the slit edges hang apart instead of meeting.
Drape and bias stretch. Viscose and rayon stretch as they hang, most of all on the bias. One sewing guide advises letting curved viscose skirt hems drop overnight and trimming them back into shape before hemming, and pre-washing viscose on a cool setting before cutting. If a viscose dress is hemmed before the panels settle, one side of the slit can end up longer than the other. The slit then looks open even when the wearer stands still.
Seam allowance at the slit. The slit edges on a skirt are made by folding back the side-seam allowance. If that allowance is narrow, the folded edge has little weight. It rolls outward and the slit looks open. A narrow allowance in loose fabric also frays, and fraying weakens the slit top further. The same 1 cm minimum that Amann gives for seams is a sensible floor for the slit edge, and a wider facing lies flatter.
Riding up. A slit rides up when the skirt or dress is tight at the hip. When the wearer sits or steps, the fabric is pulled upward, and the slit opens higher than its sewn depth. More ease at the hip, or a fuller hem, reduces this more than any stitch can.
The same hanging and growth affect the whole hem of a flared georgette, chiffon or viscose dress, not only the slit edges. Why a hem dips or goes wavy, and how to level it, is covered in why chiffon and georgette dress hems go wavy.
What should you write in the spec for a kaftan, skirt or dress slit?
Write the slit as its own line in the tech pack, with its depth, its bar-tack, its reinforcement and its test. Here is a checklist you can adapt for a viscose kaftan, a cotton skirt or a midi dress:
- Slit depth. State the depth from the hem to the slit top, with a tolerance. Check it against the hem width on a fit sample: walk, sit and climb a step in it.
- Bar-tack. Name the stitch type (for example ISO 304), the tack length and width, and its position: across the slit top, through the seam allowance and the reinforcement.
- Reinforcement. For viscose, rayon, georgette or satin, specify a fused interfacing patch behind the slit top, and edge tape along the slit edges if the panels are bias-cut.
- Seam and facing. State the side-seam allowance and the slit facing width (at least 1 cm), the edge finish, and a mitred corner where the slit meets the hem.
- Hem. For drapey fabric, ask for panels to hang before hemming. For trimmed hems such as tassels or pom-poms, approve the trim weight on the sample.
- Testing after washing. Wash the sample garment first, then test. AATCC TM135 measures dimensional change after home laundering. ASTM D1683 measures sewn seam strength and slippage in woven fabrics. The method does not predict actual wear performance, so also check the slit top by eye after several washes and wears.
Making slit kaftans, skirts and dresses with KK Fashion Exports
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