Single Jersey vs. Interlock: What’s the Difference?
Updated: 4 days ago
A practical guide to knit structure, hand feel, drape, breathability, and how construction changes the way a T-shirt behaves.
Two T-shirts can share the same GSM and still feel completely different. The reason is often how the fabric is knitted.
GSM tells you how much a fabric weighs, but not how it is constructed or how it will behave. Single jersey and interlock are different knit structures that can influence hand feel, drape, airflow, stretch, recovery, and dimensional stability.
This guide explains how the two constructions differ, what those differences mean in practice, and why neither is inherently superior.
What Is Single Jersey?
Single jersey is the most common knit structure used for T-shirts.
It is formed on a circular knitting machine with a single set of needles, creating one continuous looped fabric.
One side of the cloth (usually the technical face) shows the characteristic V-shaped loops; the reverse side has a more horizontal appearance. The structure is relatively open and flexible. It drapes naturally, feels soft against the skin, and offers meaningful stretch with relatively limited recovery. Because the fabric is essentially one layer of loops, it tends to be lighter in hand for a given yarn and can roll at the edges when cut.
Single jersey is the foundation of most everyday T-shirts.
Its openness allows good airflow, and its relative simplicity makes it responsive to finishing processes that alter softness, surface character, and dimensional stability.
What Is Interlock?
Interlock is a double-knit structure.
It is produced with two sets of needles that create two interconnected layers of loops locked together.
The result is a denser, more stable fabric with a smoother, more uniform surface on both sides. Interlock has greater inherent body and resistance to curling at the edges. Interlock often feels more stable and controlled, with stretch and recovery characteristics that differ from single jersey depending on yarn, density, and construction.
Interlock is engineered for a different set of behaviors: greater stability, a cleaner surface, and a more controlled drape. It is commonly used when a brand wants a fabric that feels denser and more self-supporting without necessarily increasing GSM through heavier yarns alone.
Single Jersey vs. Interlock: What Actually Changes?
Comparison | Single Jersey | Interlock |
Construction | Single-knit structure | Double-knit structure |
Appearance | Face and reverse often differ | Both faces often look similar |
Cut edges | May curl when unfinished | Generally curls less |
Surface | Distinct knit grain | Often smoother on both sides |
Stretch | Depends on yarn and density | Depends on yarn and density |
Drape | Can range from fluid to substantial | Often more stable under comparable specifications |
Quality | Neither inherently superior | Neither inherently superior |
Even at the same GSM, the two constructions create different relationships between weight, thickness, and tactile presence.
A 300 GSM interlock and a 300 GSM single jersey will not feel or hang the same way. The same is true at 420 GSM.
Can Single Jersey Be Heavyweight?
Yes.
A heavyweight fabric does not have to be interlock.
Heavyweight single jersey is entirely achievable through appropriate yarn selection, tighter stitch construction, controlled fabric density, and careful finishing.
When engineered correctly, it can deliver substantial body, architectural drape, and long-term shape while retaining the characteristic softness and airflow advantages of the single-jersey structure.
The misconception that “heavyweight equals interlock” overlooks how much control modern knitting and finishing allow over a single-jersey platform.
Weight and knit structure are independent variables. One does not dictate the other.
Is Interlock More Premium Than Single Jersey?
Not automatically.
Neither construction is inherently superior. Quality depends on the complete system: fiber selection, yarn quality, stitch density, finishing processes, pattern geometry, seam construction, and the intended use of the garment.
A carefully developed heavyweight single jersey can outperform a poorly executed interlock in softness, drape, breathability, and real-world longevity.
The reverse is also true.
Knit structure is a design decision, not a quality ranking.
The better question is always what behavior the garment needs from the fabric.
A Brand-Specific Example, A Note on Heavyweight Single Jersey
Heavyweight single jersey is achievable.
Weight and knit structure are separate decisions: a fabric can be heavy without being interlock, and interlock is not automaticallymore “premium.”
REALLY COOL® builds its core heavyweight T-shirts on high-density single jersey at 420 GSM for a specific balance of structure, movement, and hand feel. That is a product-architecture choice, not a claim that single jersey is always better.
For the engineering reasoning behind that choice, see Why 420 GSM Single Jersey Changes the Way Heavyweight Apparel Is Engineered.
The decision was not “single jersey is better.”
It was “this construction delivers the exact combination of properties our product architecture requires.”
The Right Knit Structure Depends on the Garment
Single jersey and interlock are not competing versions of the same fabric.
Single jersey and interlock are different knit constructions, not a ranking of quality.
Their performance depends on fiber, yarn, density, finishing, pattern, construction, and intended use. The right choice is the one that delivers the behavior required by the garment.
Single jersey often favors a more open hand, softer drape, and a familiar jersey grain. Interlock often favors a denser, more stable hand and a cleaner surface on both sides.
Single jersey and interlock are different knit constructions, not quality grades.
The right choice depends on the wearer’s needs and on how fiber, yarn, stitch construction, finishing and garment design work together.
To understand jersey more broadly, start with What Is Jersey Fabric?
For why REALLY COOL® developed 420 GSM heavyweight single jersey and French Terry, read our material-development article.
