What is interlock

Short answer: Interlock is two layers of single jersey knitted together into one fabric. The result is identical on both sides, denser and more stable than ordinary jersey. That is why it is often used for clothes that need to sit neatly and keep their shape close to the skin.

Two layers in one

In interlock two layers are knitted at the same time, and the stitches of the two layers interlock. The stitches hold each other in place, so the fabric neither curls at the edge nor frays easily. That makes interlock easier to sew and more stable in use. Stability also matters in things that take hard daily wear, like socks for men.

The same on both sides

Front and back are both smooth, because each layer turns its smooth side outwards. That feels nicer against the skin, and there is no rough back that feels different. In practice you can hardly tell which side is the front. That makes interlock a good fit for clothes where the inside matters as much as the outside.

Heavier but more stable

Interlock weighs more than single jersey because it has two layers. In return it keeps its shape much better. It does not bag out as easily at the knees and elbows, and it twists less after washing. The denser fabric also feels fuller in the hand and drapes a little firmer than a thin jersey.

A little warmer than jersey

Because interlock is denser and heavier, it holds warmth slightly better than single jersey. The air between skin and fabric stays put instead of being swapped out. That makes interlock comfortable on cooler days and in the evening. On very warm days, a thinner single jersey can be the more airy choice.

Why interlock is used for underwear

Underwear sits directly against the skin for many hours at a time. Here it helps that the fabric is smooth on both sides, keeps its shape and does not curl at the edges. An edge that curls can press and feel uncomfortable. Interlock stays where it should and gives a calm, even look all day.

How to recognise interlock

Look at both sides of the fabric. If they look the same and you cannot find a rough back, it is probably interlock. Gently pull at an edge: interlock does not roll up the way single jersey does. The fabric also feels a little thicker and more compact when you hold it between your fingers.

Caring for interlock

Interlock handles a normal gentle wash. Wash at a low temperature, turn the garment inside out and let it dry on a line or flat. Because the fabric is denser, it takes a little longer to dry than thin jersey. Avoid high heat, which can weaken fibres and elastic. The same goes for bamboo socks and other everyday items.

When to choose which

If you want something light and airy, single jersey is the natural choice. If you want something that keeps its shape and is smooth on both sides, interlock is better. Many people use both: thin layers for warm days and denser ones for the rest of the year. Think about use and season, and you will soon find the right one. See socks for men and women.

Frequently asked questions

What is the difference between jersey and interlock

Jersey is a single layer with two different sides. Interlock is two layers knitted together and is the same on both sides, denser and more stable in use.

Is interlock warmer

Yes, slightly. It is denser and heavier, so it holds warmth better than single jersey, which is the lighter and more airy choice.

Why is interlock used for underwear

Because it is smooth on both sides, keeps its shape and does not curl at the edges, which matters close to the skin for many hours at a time.