Single Jersey Fabric Vs. Interlock Fabric

Ever cut into a soft-looking knit only to find it curling at the edges, skewing after one wash, or stretching out around the neckline after two wears? Yeah, we’ve all been there. It’s usually not the sewing—it’s the fabric choice.

What Is Single Jersey Fabric?

Single jersey is the most common weft-knit structure you’ll encounter. It’s made with one set of needles, producing a smooth face (typically the “right” side) and a ribbed back. Think of your basic cotton t-shirt—chances are, it’s single jersey.

It’s lightweight, breathable, and drapes well, which makes it ideal for tees, dresses, and casual tops. But that simplicity comes with trade-offs.

• GSM Range: 120–180 g/m² (light to midweight)
• Stitch Density: ~14–18 wales per inch, 20–26 courses per inch
• Needle Recommendation: 70/10–80/12 ballpoint or stretch needle
• Shrinkage: Can shrink up to 8% if untreated—pre-washing is non-negotiable

The face side is smooth and flat; the back shows horizontal ribs. Because it’s asymmetric, it curls—especially at hems and necklines. This isn’t a flaw; it’s physics. The tension imbalance between face and back pulls the fabric into a roll.

I once skipped pre-washing a single jersey dress for a client sample. Big mistake. Post-wash, the hem curled so aggressively it looked like a scroll. Lesson learned: stabilize or pre-treat.

What Is Interlock Fabric?

Interlock is a double-knit structure—two single jerseys knitted together back-to-back. It’s like two layers of jersey fused during knitting, not after. The result? Both sides look identical: smooth, flat, and stable.

Because it’s symmetric, interlock doesn’t curl like single jersey. That makes it a go-to for structured knits, baby clothes, and elevated basics.

• GSM Range: 180–280 g/m² (mid to heavy)
• Stitch Density: ~16–20 wales per inch, 30–40 courses per inch
• Needle Recommendation: 80/12–90/14 stretch or jersey needle
• Shrinkage: Typically 5–7%, but high-quality interlock can hold under 4%

It’s heavier and less stretchy than single jersey, especially crosswise. That reduced elasticity gives it better shape retention—but also makes it less forgiving on curved seams.

Pura Fabric once supplied a custom interlock for a loungewear brand that wanted the drape of jersey but the polish of a woven. We adjusted the yarn twist and stitch length to reduce torque, which helped with cutting alignment. The mill later told us it was one of their trickiest runs—but the fabric held its width beautifully during production.

Structure & Knitting Process

How Single Jersey Is Made

Single jersey is knitted on a single needle bed—usually a circular knitting machine with latch needles. Each needle forms one loop per course. The front loops create the smooth face; the back loops form the ribs.

Because only one set of needles is used, the process is fast and cost-effective. But the asymmetry causes inherent instability.

One issue we see often: stitch laddering in single jersey side seams. It happens when the fabric is pulled during sewing, especially with fine yarns. To prevent it, use a walking foot, reduce presser foot pressure, and stitch with a 2.5–3.0 mm stitch length.

Also, avoid long stretches of straight stitching without securing. I once had a run of tees where the side seams unraveled after two wears—turns out, the overlocker wasn’t properly tensioned for the 30s count cotton we were using.

How Interlock Is Made

Interlock requires a double-bed knitting machine. Front and back needles work alternately, creating interlocking loops. One course is formed on the front bed, the next on the back, linking them together.

This double-layer construction takes more time and yarn, so it’s pricier to produce. But the payoff is stability.

Because both sides are identical, interlock lays flat and resists curling. It also handles higher heat during finishing—critical for sanforizing or resin treatments.

A note on pressing: interlock can handle a warm iron (cotton setting), but always use a press cloth. I’ve seen shiny marks appear on dark interlock from direct heat—ruined three samples in a row before I switched to a silk organza press cloth.

Stretch & Recovery Behavior

Single jersey stretches more—especially crosswise. You can get 40–60% stretch across the grain, but recovery is only so-so. Over time, especially with lower twist yarns, it can bag out at elbows or underarms.

• Crosswise Stretch: 40–60%
• Lengthwise Stretch: 10–20%
• Recovery Rate: ~75–85% after 5 wears

Interlock, by comparison, stretches less—30–40% crosswise—but recovers better. The double structure resists deformation.

• Crosswise Stretch: 30–40%
• Lengthwise Stretch: 10–15%
• Recovery Rate: ~90%+

Here’s a real-world test: I once compared two black knits for a capsule wardrobe. Single jersey felt softer initially, but after five washes, the neckline sagged. Interlock held its shape, though it took more effort to sew through the thickness.

If you’re designing a fitted crewneck, interlock’s better recovery might be worth the extra sewing challenge.

Drape & Fabric Hand

Single jersey drapes fluidly. It clings and moves with the body—great for slinky dresses or flowy tunics. The hand is soft, especially with combed cotton or modal blends.

But that drape comes with a catch: it can cling in unflattering ways. A 140 gsm single jersey in 100% cotton might feel dreamy, but it’ll show every contour and wrinkle easily.

Interlock has a more structured drape. It holds its shape, skims the body, and resists wrinkling. The hand is firmer—some call it “crisp” when new, though it softens with wear.

One designer I worked with wanted a “knit that feels like a woven.” We tested a 240 gsm interlock with a mercerized finish. It pressed beautifully, held sharp edges, and didn’t collapse at the shoulders. Not as soft as single jersey, but way more polished.

Stability & Edge Behavior

Single jersey curls. A lot. At hems, necklines, and cut edges, it rolls toward the back (ribbed side). This isn’t just annoying—it can throw off your seam alignment if you’re not careful.

To manage it:

• Use spray starch or knit stabilizer on cut edges
• Pin frequently when sewing
• Consider a twin needle for hems to balance tension

Interlock? It barely curls. Cut it, and it stays put. That makes it easier to cut in large batches and more predictable during assembly.

But don’t assume it’s foolproof. Thick interlock can still shift if pulled unevenly on the bias. I once had a batch of pajama pants where the legs came out mismatched—turns out the fabric was slightly skewed from uneven tension during dyeing. Always check the grain before cutting.

Sewing & Garment Construction Tips

Needles & Threads

For single jersey:

• Needle: 75/11 or 80/12 ballpoint
• Thread: Poly-core or textured polyester (stretch thread)
• Stitch Length: 2.5–3.0 mm (straight stitch), 1.5–2.0 mm (zigzag)

For interlock:

• Needle: 80/12 or 90/14 stretch
• Thread: Heavy-duty poly or cotton-wrapped poly
• Stitch Length: 3.0 mm (straight), 2.0 mm (overlock)

Skip the universal needle—seriously. I’ve seen skipped stitches and snags from using the wrong tip. Ballpoint or stretch needles have a rounded tip that pushes fibers aside instead of piercing them.

Seam Finishes

Single jersey benefits from:

• Overlocked seams (3 or 4-thread)
• Coverstitch hems
• Stay tape on necklines

Interlock can handle:

• Clean-finished folded hems
• Twin needle topstitching
• Even French seams in lightweight versions

One trick: for interlock neckbands, cut the ribbing 10–15% shorter than the neckline. It creates the right tension without puckering.

Case Study: Choosing Fabric for a Sustainable Activewear Line

A small activewear brand approached us needing a knit that balanced breathability, durability, and eco-credentials. They wanted something soft but structured—no sagging after workouts.

We tested three options:

• 160 gsm organic cotton single jersey
• 200 gsm TENCEL™/cotton interlock
• 180 gsm recycled polyester jersey

The single jersey felt best initially, but failed recovery tests—necklines stretched after 30 minutes of movement. The recycled jersey held shape but felt plasticky.

We went with the TENCEL™/cotton interlock. It wasn’t the softest, but it resisted odor, held its form, and had a luxe hand after washing. The supplier had to adjust the stitch length to prevent tunneling on the overlock, but once dialed in, production ran smoothly.

Trade-offs? Higher cost, slower sewing, and less drape. But for their market—yoga and low-impact training—it was the right call.

Case Study: Fixing Skewed Hems in Childrenswear

A children’s brand using 160 gsm single jersey kept getting twisted hems on bodysuits. The factory blamed the fabric; the designer blamed the pattern.

Turns out, it was both.

The fabric had a 3% skew after dyeing—barely noticeable until cut and sewn. The pattern had straight hems, but the body was cut on grain. When the skewed fabric was sewn, the stress pulled the hem into a spiral.

Solution:

• We requested the supplier improve their de-skewing process (steaming + tension control)
• Redesigned the hem to follow the bias slightly
• Added a stay tape at the seamline

It took three rounds, but the final run was clean. Lesson: fabric behavior and pattern geometry have to align—literally.

Micro-Note: Pressing Knits

Don’t iron knits like wovens. Use a press-and-lift motion. Steam helps, but too much can stretch the fabric. I keep a wool pressing mat for knits—it gives a little, so I don’t flatten the texture.

Final Thought

Choosing between single jersey and interlock isn’t about which is better—it’s about what kind of problem you’re okay with solving. Single jersey gives you drape and ease but demands careful handling. Interlock offers stability and polish but can feel stiff if you’re not used to it. I’ve ruined garments with both. I’ve also made some of my best pieces with both. Know the trade-offs. Test first. Then sew like you mean it.