Denim is a type of twill fabric made from cotton. It is typically yarn-dyed with indigo, creating the classic blue color associated with jeans. It can be woven on either a shuttle or projectile loom. Most twill fabrics go through several different processes to achieve their final appearance. Some common dry methods include washing, brushing and sanding.

Cotton

Denim is a durable cotton-based fabric that is woven in a twill pattern. This twill is usually yarn-dyed with indigo to create the classic blue color we associate with jeans. Historically, this type of cloth was made for sailors and dockers who needed sturdy work pants that could withstand rough weather conditions. Today, the fabric is still primarily made from cotton but may contain a small percentage of stretchy fibers like spandex or elastane. It adds elasticity to the finished woven garment, which is useful in creating stretchy jeans and other clothing pieces that require stretching.

In addition to the fabric, denim also requires much water for production. It is estimated that 5,700 liters of water produce one pair of jeans. It is a significant environmental burden, especially when the average American wears four pairs of jeans yearly. Once the fiber is spun into yarn, it can be woven on a shuttle or projectile loom. A shuttle loom produces selvage denim, where the weft thread passes under two warp threads for each row. Projectile looms, on the other hand, use a single weft thread for each row. This style of denim can have a more delicate edge that needs to be carefully sewn to prevent fraying.

Dyeing

The process of dyeing denim fabric is complex and requires a lot of time. It involves soaking yarns in a liquid that contains a colorant (dye). In the case of denim, the pigment is usually indigo.

The yarns are then spun into threads. Once the lines are ready, they can be woven into denim. The most common weaving patterns for jeans are left-hand and right-hand twills. The fabric may have a different texture and feel depending on the threads’ fineness. During this step, the cotton fibers are often subjected to harsh chemicals that harm human health and the environment. The cotton is also often grown using pesticides and herbicides. It is why it’s important to look for manufacturers that prioritize free trade and sustainability. Before the looms begin weaving, the warp yarns must be dyed. There are two ways to do this: rope dyeing and sheet dyeing. Both processes are water-intensive and require a lot of energy.

The dyes used for denim are typically reactive and oxidized by a hot caustic soda solution in hydrogen peroxide. It helps the dyes bind to the cotton fibers. The oxidation process also allows the dyes to set in the yarn, ensuring that they won’t wash out with regular washing.

Weaving

A lot of work goes into the production of denim. From the cultivation of cotton to the dyeing and finishing processes, it’s a testament to the ingenuity of the textile industry that such a versatile fabric can be made. The material is a sturdy cotton warp-faced cloth woven with a diagonal ribbing that gives it its trademark appearance. It’s often yarn-dyed with indigo and woven to create the classic blue shade, but other shades are also used, including black (produced through sulfur dyeing). It’s usually woven using right or left-leaning threads depending on whether it’s warp-faced or weft-faced. Weft-faced denim tends to be more flexible and softer but may have different structural integrity than warp-faced denim.

One of the most important factors in the look and feel of denim is the weaving technique. In particular, the ’twill’ weave gives it that unique diagonal ridged texture and makes it thick and hardwearing. The most common twill for denim is a three-by-one right-hand twill, which means there are three warp threads for every weft thread on the face of the fabric. The yarns are then woven together on a shuttle loom. The type of twill and the weaving pattern can determine a lot about the final fabric, including its strength and flexibility, how it feels and how it will fade. Some more modern materials are made with stretch fibers such as elastane or spandex, making them very comfortable to wear straight off the loom and great for fitted jeans.

Finishing

Denim is made in a specific weave pattern that gives it strength and durability. Typically it’s woven on a shuttle loom with a warp thread and a weft thread. When this technique is used, it’s referred to as selvage denim. This type of denim has a distinct edge where the weft thread reverses direction at the end of each row. The weft threads are typically dyed blue with indigo, a natural dye that produces the classic blue color associated with jeans. The weft yarns can also be wrapped with spandex fiber. It allows the woven fabric to stretch and will often cause it to be more flexible than straight cotton fabrics.

In some cases, the elasticity of the denim can be increased even further by adding more spandex to the warp yarns. It can greatly improve stretchy denim jeans, which many prefer over stiff and brittle materials. Creating denim is still complex, with many issues surrounding environmental impact and ethical concerns, from pesticides that can lead to worker exploitation to the chemicals used in the dyeing processes, known to release harmful substances like carcinogenic amines. With new technology, though, the production of denim is becoming more sustainable and eco-friendly.

Paul Petersen