Fabric 101: Interlock Knit

Interlock fabric is a double-knit jersey that is known for being a reversible medium-weight type of knit fabric. In general, it tends to be more stable and structured than the thinner single-knit jersey fabric and is, therefore, more often used for bottom-weight garments or knit clothing that has a stiffer drape.

Fabric	Interlock
Texture?	Smooth or more cotton-like depending on the fiber used
Stretch?	Usually greater than 25% stretch crosswise with very little or no stretch lengthwise
Heavy or light?	Medium weight
Stiff or drape?	Usually has a heavy drape, but it’s not flowy
Nap?	Usually no nap
Typical fiber content?	Can be anything, typically cotton or polyester
Opaque or sheer?	Opaque
Shiny?	Not shiny, but a slight sheen depending on the fiber used
Fraying?	Does not fray
Pilling?	Pills easily
Other identifying properties?	It’s reversible and has a double layer of jersey
Cool or warm weather?	Better for cool weather
What to make?	Long-sleeved T-shirts, polos, structured knit dresses, cardigans, joggers, pants, and any type of knit garment that needs some structure
What needle to use?	Jersey needles in size 80 or 90

What kind of fabric is Interlock?

Interlock material is a double-knit jersey fabric. To oversimplify, this basically means it’s made up of two layers of jersey that have been mended together. This gives the fabric more strength and durability but is generally at the expense of stretchability and flowy drape.

This means interlock knit fabric is thicker and more structured than the typical jersey fabric. While it tends to have considerable stretch across the grain, there is usually very little elasticity, if any, along the length of the fabric. 

Interlock also gives more coverage than thinner knit fabrics. Since it’s two layers, the fabric is opaque and can be used for pants, skirts, and tops without having to worry if anyone will see your undergarments.

What can you make with Interlock fabric?

Interlock fabric is used for medium-weight knit garments that need more structure or strength than jersey fabric. Most commonly, it’s used for long-sleeved or heavy-weight T-shirts, as well as joggers and jackets. However, interlock can be used for just about anything. It’s not as flowy as jersey fabric, but it can still be used for skirts and dresses that have a heavier or more structured drape.

Properties of Interlock knit fabric

• Texture: The texture of interlock fabric is determined by the type of fiber that’s used to make it. For example, if the material is made from polyester, the fabric will be fairly smooth to the touch. If the material is made of cotton, it will usually have a softer slightly fuzzy texture (similar to the texture of a standard T-shirt).
• Stretch: While interlock fabric is typically not as elastic as jersey fabric, it still has some stretch across the grain. You can usually expect at least a 25% stretch crosswise on interlock fabric. However, if there is any stretch lengthwise at all, it’s a very small amount.
• Weight: Interlock fabric is a medium-weight knit material. This is because it is a double-knit and has two layers.
• Drape: Interlock fabric has a somewhat moderate drape as well. It’s not stiff like standard woven quilted cotton fabric, but it’s not flowy and airy like lightweight fabrics are.
• Fiber composition: Interlock fabric can be made from just about any kind of fiber. However, it’s most common to find it made from polyester or cotton.
• Opacity: Since it’s a double-knit fabric, interlock material should always be opaque.
• Shine: Interlock is generally a matte fabric. However, there may be a very slight sheen to the surface depending on the type of fiber used. Polyester will be more likely to have this reflective property than cotton.
• Fraying: Interlock is a knit fabric, so it does not fray the way woven fabrics do.
• Pilling: One of the downsides of working with interlock fabric is that it is prone to pilling (don’t let any velcro get near this fabric!). It also easily gets caught on things, causing snags.
• Wrinkling: Overall, interlock fabric is wrinkle-resistant. It can wrinkle if it’s made with a natural fiber (cotton, wool, etc.), but it usually holds up pretty well.
• Reversible: Interlock is the same on both sides of the fabric. Sometimes if a pattern is printed on the fabric, it will only be on one side. However, the actual weave of the fibers is reversible.
• Breathability: Interlock is not as breathable as jersey fabric since the double layers do not let as much airflow. Natural fibers will make the material more breathable than polyester.

How to sew with Interlock fabric

In my opinion, interlock fabric is one of the most difficult knit materials to sew with, especially if you’re using a standard sewing machine and not a serger. This is because the thickness of the fabric causes it to stretch out a lot when going through the feed teeth and presser foot. 

But that doesn’t mean it’s impossible to so, even if you don’t have a serger, you can try some of these tips to get your sewing machine to work for you:

• Changing the pressure settings on the presser foot so that it’s not clamped down as tightly.
• Adjust the top thread tension on your sewing machine
• Try installing a walking foot on your sewing machine
• Use a knit presser foot
• Apply wash-away tape to the seam before sewing
• Place a piece of tissue paper on top of the seam as you sew

Interlock fabric also needs to be sewn with a jersey needle (also called a ballpoint needle), and you want to switch to a zigzag or lightning-bolt stitch on your sewing machine. (A straight stitch will end up with snapped thread as soon as you try to stretch the fabric along the seam)