What Is Interlock Knit Fabric?

Interlock knit is a type of fabric that consists of two layers of knit jerseys that interlock together. Most often, one side will have some texture while the other will be smooth.

Today, we’ll learn more about the properties of this fabric, how to sew and care for it, as well as where to shop for it. Without further ado, let’s get to it.

A Brief Walk-Through Time

The industrialization of the textile industry in the 19th century introduced knit fabrics as we know them today. Originally, they were reserved for making shirts and underwear for sailors, soldiers, and laborers. This remained the case until none other than the Coco Chanel took a glance at a French sailor and his striped shirt and had a lightbulb moment. 

It would take several decades for knits to gain even more popularity. When baby boomers came along, they became the first generation of teenagers that could enjoy their disposable income. This meant that they started indulging in mass-manufactured clothing and pleasure activities, which knits were absolutely perfect for. 

Interlock is almost as old as the modern jersey, and it became a favorite to the glitterati of the roaring 20s who popularized polos made out of this fabric. 

What Is Interlock Knit Fabric Made Of?

Interlock can be made out of any fiber, but the process is what matters.

Regular jerseys are the same stuff that your grandma produces when she’s making a Christmas sweater. It’s a series of interconnecting loops that have smooth knit stitches on one side and bumpy purl stitches on the other. The knitting machines that are making the fabric don’t use knitting needles, but a series of hooks and combs that are not too different from ones you will find on those knitting toys from craft and big box stores. 

The process for making interlock is slightly more complicated. To put it simply, the machine creates two layers of jersey, then introduces another thread that loops between two layers and connects them. 

Below are two videos that will hopefully make this segment a bit clearer. The first one shows how the regular knit jersey is made, and the second shows how two knit jerseys connect to create interlock knits. 

Knitting | Loop/Stitch formation | Cotton machine | Straight bar frame | Spring bearded needle
Operation of LATCH needle in knitting process: DOUBLE FABRIC WITH SWING ACTION

Is Interlock Similar to Double Knit Stitch in Knitting?

Though interlock is also sometimes called double knit, it’s completely different than the knitting stitch of the same name. The most important difference is that the space between two layers of outward-facing knit is hollow, while the interlock has threads connecting one side to another. 

If interlock were made in the same fashion as the double-knit stitch fabric, if you were to cut into it, you could peel the layers one from another. 

What Is Interlock Fabric Used For?

Interlock knits are most often used for sportswear and activewear. Due to its properties. it’s perfect for leggings, sweatshirts, and sports bras. It’s also regularly used in the production of T-shirts, polos, and dresses.

Benefits of Interlock Knit

First and foremost, interlock knits are heavier and sturdier. This not only allows them a wider application, but also makes everything made out of these fabrics feel more expensive. 

They recover beautifully after being stretched. They are very durable, and some versions have moisture flicking properties. This makes them ideal for making sportswear and undergarments for people with very active jobs. This type of fabric is equally suitable for the production of everyday garments, like dresses or polos. Those garments end up with all the benefits of knit fabric (easy to fit, doesn’t wrinkle), with the look of a woven one (crisp lines, substantial feel). 

And last but no way least, this fabric is ideal for beginners. In fact, if you’re planning your very first knit fabric project, use an interlock knit fabric. Though there are still a few things you have to take into consideration when working with this fabric, at least it doesn’t curl and slide around like regular jersey. Plus, you can get great results even when using a basic mechanical home sewing machine. 

Is Interlock Knit Fabric Stretchy?

Interlock is one of the stable knits, which makes it stretchy widthwise and not lengthwise. It has more stretch than a regular jersey and less than ribbing, with a very good recovery.

What Is the Difference Between Jersey Knit and Interlock Knit?

Though one is actually made out of two layers of the other, they look and behave completely differently, and are better suited to different projects.

To start with, the jersey is lighter and drapes better, while the interlock is sturdier and can even provide some structure (if it’s heavy enough).

Interlock is also stretchier and has a better recovery rate. It’s also reversible, white jersey has a clear right and wrong side (knit and purl side, as in regular knitting).

There’s also a big difference in how they behave over time. Jersey is more likely to deteriorate with regular wear and washing, while interlock is a lot more durable. It’s also easier for the interlock to come in a variety in weights, while jersey at some point crosses over into sweater knits.

Jersey knits are also easier and take less time and resources to produce, so that’s one of the reasons why they usually cost less (even when you compare the same weights of jersey and interlock). 

How Do I Know If My Fabric Has Interlock?

At first sight, you will notice some texture. Most often, the fabric is completely reversible and both sides are supposed to have rows and rows of tiny dips.

Next, it’s time for the stretch test. Stretch the fabric horizontally (selvage edge to selvage edge). If it doesn’t curl, it’s interlock. But if it does, it’s a regular knit jersey.

How To Care for Interlock Knits Fabric

Just like with any type of fabric, the fibers are more important when it comes to deciding how to care for interlock knits. Natural fibers can handle more heat than synthetic ones.

That being said, your best bet is to wash the fabric in cold water. That’s the best way to preserve both the fibers and the color for as long as possible. Of course, you also have to use a detergent that is suitable for the job, so make sure to check out the working temperature range on the packaging.

The drying is where you can do some serious damage to the interlock (as well as other knits). Ideally, you should air dry it, but this as well can cause some damage if not done right.

One of the best things you can do for any knit before drying is to put them on one more spin cycle. This will wring out all excess water and we don’t want that water since it will weigh down and stretch out the fabric. If possible, also try to dry each piece flat. If you have to hang them, try to avoid clothespins and just throw the garment over the clothesline.

There’s no need to iron it, and you can literally shake off any visible wrinkles.

In case of stains, apply a solution that is suitable for the fiber the fabric is made from. However, try to avoid rubbing too hard because you can stretch out the area.

If you have pets, watch what their little paws, and especially claws, are doing. Though interlock is more durable than the regular jersey, just one puncture can cause a hole to appear and grow. This goes in particular for both athletic and leisurewear, because those types of clothes are tugged and pulled all the time. You can do some basic darning to fix the hole, but it will change how the fabric behaves in that area.

Where to Buy Cotton Interlock Knit Fabric

You can easily purchase interlock knits online, but it may be a good idea to do it in a brick-and-mortar store first. Online fabric purchases can go very wrong because you can’t get the feel of the fabric without touching, not to mention that your monitor settings could be showing a different color to the one that’s happening in reality.

If you have a fashion or a garment district anywhere nearby, this is your best option. These districts often have whole streets filled with fabric stores that will provide you with numerous choices and deals.

Your local fabric or sewing supply store should be properly stocked as well. With a rise in the popularity of knits amongst home sewists, many stores offer better stock and options than they did only a decade ago.

Is The Production of Interlock Sustainable and Ethical?

The answer is that it’s ethical and sustainable as much as any other fabric. The only thing that can be said is that it doesn’t include humans in one stage of its production since human hands can’t knit with such fine threads.

If this is a very important issue for you, you can always seek out fabrics with the Fair Trade seal of approval. To learn more about what to look for and what that mark entails, check out this document.

How to Shop for Good Interlock Fabric

This is where shopping in person comes in handy. The best way to check if the interlock fabric is any good is to test its recovery. As the term implies, you are looking at the fabric’s ability to recover after being stretched. Right next to its weight and feel, this is the most important sign of a decent bolt of interlock.

If you must shop online, avoid any terms that communicate lightness like “featherweight”. You want to see at least “midweight”, or even better, “hefty” or ‘beefy” amongst the fabric’s descriptors.

Sewing Interlock Fabric

All knits prefer a serger and a cover stitch machine, but a decent home sewing machine can do good work from interlock as well. Actually, when making sportswear, a triple straight stitch from any regular home sewing machine will provide both elasticity and strength. Other than that, any other stitch that works for you when sewing knits will be good for interlock as well.

Even when working with cotton, it may be a good idea to pick polyester thread. It’s far more likely to endure the friction caused by the speed of a serger. By the way, you should also work at maximum speed on a regular sewing machine to prevent the seams from stretching out.

Avoid using a 2-ply thread that might be in your serger because it’s not strong enough for the projects you’ll make from interlock. The 3-ply is usually a good choice, though avoid anything metallic or glittery since they can wear against the fabric and cut the threads it’s made from.

But before you start sewing, make sure to prepare fabric properly. Although it’s better to wash your interlock knit garments in cold water, you should go for the maximum temperature the manufacturer recommends when preshrinking the fabric. This information will either be right next to the bolt in the store, in the product description online or printed out on the receipt.

As for marking, any of your favorite methods will be okay. However, if you’re doing thread marking, make sure you’re using ballpoint needles. Just the same as you should use ballpoints to sew the fabric itself, as well as ballpoint pins when pinning the fabric. Sharps may puncture and break the thread, while ballpoints gently nudge it away and prevent the formation of holes.

Rotary cutters will give you the best results when cutting interlock, but if you don’t have them (or you don’t have space for a cutting mat) regular tailoring shears will do. Make sure that they are very sharp and that you work in long fluid motions.

If you are struggling to work with this fabric, you can always starch it to stabilize it. After preshrinking it, just treat it to a spray of starch so it stiffens a little. Or, if you live in an area with very hard water, just skip on the fabric conditioner and use cheap laundry detergent, and the fabric will come out stiff and crinkly already.