Interlock fabric is a double-knit material used primarily for baby clothing, t-shirts, underwear, activewear, and lightweight home textiles. Its smooth finish on both sides, natural stretch, and resistance to edge curling make it one of the most versatile knit fabrics for both ready-made garments and home sewing projects.
What Makes Interlock Different From Other Knits
Interlock is constructed on a knitting machine with two needle beds, producing what’s essentially two layers of single jersey knitted together back to back. This double-layer structure gives it a few properties that set it apart from the single jersey you’d find in a basic t-shirt. It’s thicker, heavier, and firmer, yet still soft and stretchy. Most interlock fabrics fall in the range of 170 to 250 grams per square meter, depending on the yarn and stitch length used.
The easiest way to identify interlock is to look at both sides of the fabric. Single jersey has a clear “right” and “wrong” side, with visible V-shaped loops on the front and horizontal bars on the back. Interlock looks identical on both sides, with smooth V-shaped loops everywhere. The other giveaway: if you stretch it horizontally, the edges won’t curl. Single jersey curls noticeably at cut edges, which is why interlock is the preferred choice for free-cut and laser-cut garments where hems aren’t finished.
Baby Clothing and Innerwear
Interlock’s biggest reputation is in babywear. Onesies, rompers, leggings, and baby sleepwear are commonly made from cotton interlock because the fabric is smooth on both sides, meaning no rough textures sit against a baby’s skin. There are no seam-catching loops or textured backsides that could cause irritation or chafing.
The natural stretch is especially important for infants who are crawling, rolling, and constantly moving. Interlock stretches to accommodate movement, then recovers to its original shape afterward. This stretch comes from the knit structure itself, not from added elastic fibers, which keeps the fabric breathable. The double-knit construction also makes it more durable than single jersey, so it holds up through the frequent washing that baby clothes demand.
Everyday Apparel
Beyond baby clothes, interlock is widely used for adult t-shirts, polo shirts, undershirts, and casual tops where a slightly more substantial feel is desirable. The fabric drapes well without being flimsy, and the identical front and back make it forgiving during construction. It’s also a go-to for leggings, yoga pants, and other fitted activewear because it stretches in multiple directions while maintaining good shape retention over time.
Dresses, tunics, and lightweight cardigans often use interlock as well, particularly in cotton or cotton-blend versions. The fabric’s stability means garments keep their silhouette rather than stretching out and sagging after a few wears. For anyone who’s been frustrated by a jersey top that twists at the side seams or loses its shape by the afternoon, interlock solves both problems.
Home Textiles and Other Uses
Interlock isn’t limited to clothing. It shows up in mattress covers, sofa linings, upholstery backing, and pillow covers where a soft, stretchy layer is needed. Bags and accessories sometimes use heavier-weight interlock as a lining fabric. The non-curling edges and smooth surface on both sides make it practical anywhere the fabric’s cut edge might be visible or where comfort against skin matters.
Sewing With Interlock at Home
If you’re planning to sew with interlock, it’s one of the most beginner-friendly knit fabrics. The edges don’t curl when cut, so the fabric lies flat on your cutting table and feeds through a sewing machine without fighting you. That alone makes it far easier to handle than single jersey.
Use a ball point needle (sometimes called a jersey needle) in size 75/11 to 90/14. Ball point needles slide between the knit loops rather than piercing through them, which prevents small holes and runs. Polyester thread works well because it has a slight stretch that moves with the fabric rather than snapping under tension. A narrow zigzag stitch or a stretch stitch on a standard sewing machine will give your seams the flexibility they need. A serger works beautifully with interlock but isn’t required.
One important step: pre-wash your fabric before cutting. Cotton interlock typically shrinks 3% to 5% during its first wash. If you skip this step and sew a garment from unwashed fabric, it may shrink unevenly after its first trip through the laundry. Wash in cold water on a gentle cycle and tumble dry on low heat, or air dry. This mirrors the care you’ll give the finished garment and gets the shrinkage out of the way before your pieces are cut and sewn.
Common Fiber Content
Cotton interlock is the most common version, prized for breathability and softness. Cotton-polyester blends add durability and reduce shrinkage while keeping the fabric comfortable. Cotton-spandex blends increase stretch and recovery, making the fabric snappier for fitted garments like leggings. You’ll also find interlock in 100% polyester for moisture-wicking activewear, and in bamboo or modal blends marketed for extra softness.
The fiber content changes how the fabric behaves. Pure cotton interlock breathes well but wrinkles easily and shrinks more. Polyester blends resist wrinkles and hold color longer but trap more heat. Spandex blends offer the most stretch and recovery but require lower dryer temperatures to protect the elastic fibers. Checking the fiber content on the bolt or product listing tells you more about how the fabric will perform than the “interlock” label alone.