A Complete Overview of the 5 Production Stages of Making Denim
Have you ever thought about why denim is blue on one side and white on the other? Or why the colour changes when you wear and wash your jeans?
Maybe you’ve noticed that the legs of your jeans sometimes twist a little? And you’ve surely encountered jeans with stretch.
It’s all got something to do with how denim is made.
It’s a complex process with dozens of steps, each of which impacts what the final outcome will look like, how it will feel, and (very importantly) how it fade.
When you break if down, though, you get five main stages: raw materials, spinning, dyeing, weaving, and finishing.
This beginner’s guide provides an overview of how denim is made, along with links to in-depth analyses with much more information about each of the five stages.
Production Stage 1: Raw Materials
The first stage of making denim is the raw material. And denim is (mostly) made from cotton; a natural fibre that comes from the cotton plant. It’s well-suited for garment production because it’s comfortable, breathable and durable.
In developed cotton-growing countries, cotton is harvested with mechanical pickers. In developing areas, such as in Africa and Southeast Asia, picking is often still done by hand.
Once harvested, the raw cotton goes through the ginning process at the cultivation site. This separates the fibres from the seeds. After ginning, the raw fibres are compressed into bales, weighing around 250 kilos. Each bale has enough cotton for roughly 400 pairs of jeans.
Cotton’s quality is based on a set of physical properties, including staple length, fineness and maturity (known as micronaire), strength, and colour.
Visit the in-depth blog post about cotton to learn more about each of cotton’s physical properties, and how they influence your denim.
Synthetic Stretch Fibres
With slimming fits and new spinning technologies, denim makers are now using synthetic fibres as well to make denim more stretchable.
Synthetic ‘elastomer’ fibres are added in the spinning process, which is the next stage of making denim.
Spinning is the process of turning fibres into yarn.
It’s all about making the raw material fibres parallel, and then twisting them.
Before the Industrial Revolution, spinning was done by hand. These days, there are two common methods:
Ring spinning was invented in 1828, so it’s the original way. It gives a soft and uneven yarn, which results in fades with tons of contrast. And that’s a good thing.
In 1963, the new school way of spinning was invented. It’s called open-end spinning, and it’s a lot faster and cheaper. The method also creates a more even and hairy yarn, which is less durable. Regarding the look, open-end denim fades with less contrast.
Both methods have three characteristics in common: the thickness, the texture, and the twist of the yarn.
To make stretch denim, you need to add a synthetic elastomer to the yarn in the spinning process, and you get the best result with ring spinning.
That’s because the stretch is spun directly into the core of the yarn with the cotton wrapped around the elastomer. This way, you maintain the soft touch and fading capabilities of cotton, while adding stretchability.
The advantage stretch denim is that it makes the jeans a lot more comfortable. But there are downsides too.
The blog post about spinning goes into detail about the pros and cons of stretch denim.
Dyeing is where the yarn gets its colour. It’s done by soaking the yarn in a liquid that contains a dyestuff.
The classic kind of denim that is blue on the outside and white on the inside is ‘yarn dyed’—meaning only the warp yarn is dyed.
Natural or Synthetic Indigo
The original blue colour comes from indigo. It’s one of the oldest dyestuffs still in use today; in 2016, a 6000-year-old scrap of fabric dyed with indigo was found in Peru.
Indigo used to be ‘natural’ as it was made from plants. These days, however, almost all indigo is synthetic through chemical engineering.
Why Denim Fades
To get the dyestuff onto the yarn or the fabric, it’s solubilised in water. When the yarn or fabric is pulled out of the dyeing vat, the oxidation process binds the colour to the fibres of the yarn.
But the colour doesn’t reach the core of the yarn, and the dyestuff only binds externally. This gives what’s known as a ring dye effect. And that’s what makes jeans fade. As the dye slowly wears and washes off, the undyed core appears.
There’s actually also a third option: dyeing with sulfur.
It was introduced as a cost-saving measure in the 1970s, but these days, sulfur is also used to add so-called tops and bottoms on indigo-dyed yarn, as a way to create the cast.
Weaving is the process of turning yarn into fabric.
Two sets of yarn are interlaced at a 90° angle. For classic denim that’s mainly blue on the front and mainly white on the back, the weft yarn that runs across is undyed, and warp yarn that runs downwards is dyed.
Denim belongs to the twill family of weaves. The most common type of denim is a 3×1, which has three warp yarns for each weft yarn on the front of the fabric, and a diagonal twill line that runs either to the left or the right.
You’ve surely heard about selvedge denim. It’s the original way of weaving denim; connoisseurs prefer it for the great fades it yields, which is a result of the slower speed it’s woven at. It’s valued for its aesthetics and its history.
To weave, you need three motions: shedding, picking and battening. In terms of production of selvedge denim, where it differs from modern denim weaving is the picking. The relatively slow speed of this process is why modern high-speed looms were invented.
The last stage of making denim is fabric finishing. Put simply, a fabric finish is a treatment that changes the appearance, the touch, or the performance of the fabric.
They’re divided into two categories: functional finishes, which are used to correct and prevent issues of dimensional stability, and creative finishes that enhance the look and feel of the fabric.
Once a denim comes off the loom, it’s known as ‘loomstate.’ This unfinished denim doesn’t have any dimensional stability. If the fibres are not shrunk back into their original state, the denim will shrink and the legs will twist once the jeans are washed.
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