What is TENCEL™?

This is the first of a three part series on TENCEL™ Lyocell, the primary fiber used in Athletic Articles underwear. I dedicated a significant amount of R&D to the fabric I would use for my debut product line, so I thought I’d tell you why I decided on this option.

I’ve tried my best to keep this article simple, but there are details that I find crucial and don’t want to assume you’re not interested in. If you excelled in organic biology or chemistry, you’ve got a head start, but if you, like me, couldn’t at the time envision a practical application for these fields of study and need a foundational refresh, I’ve got you covered.

There are a few things to understand before defining TENCEL™, so buckle up.

Firstly, fabrics are made of yarns, and yarns are made of fibers spun together, and there are three categories from which fiber makeups can be derived: natural, synthetic, and semi-synthetic. Natural fibers are organically occurring and come from plant fibers and animal fibers. Synthetic fibers are engineered inorganic polymers originating from petroleum byproducts. Semi-synthetic fibers are organic plant fibers that are chemically processed to form new fibers.

The second thing to understand is the importance of cellulose. Cellulose is the most abundant organic polymer and carbohydrate on Earth. It forms the main structural component of plant cell walls and is stabilized by extensive hydrogen bonds within and between its chains. Cellulose is water insoluble and biodegradable. Cotton, picked right off of the plant, for example, is nearly pure cellulose.

Lastly, you’ll need to understand Lyocell. Lyocell is the generic name given to the process used to create a semi-synthetic fiber from plant cellulose. It was first developed in 1972 as an alternative to the older viscose process in rayon production which uses a neurotoxic chemical (carbon disulfide) and generates large amounts of contaminated wastewater.

The Lyocell Process
Here’s the deep dive: Wood chips are chemically digested to dissolve lignin and hemicellulose. Lignin is an organic polymer in plant cell walls that makes them rigid and woody and hemicellulose binds lignin to cellulose. After dissolving, the remaining product is a refined, pure cellulose pulp. The process until this point is essentially the same used to make paper.

The dried cellulose pulp is then dissolved in N-methylmorpholine N-oxide (NMMO) in order to disrupt the strong, insoluble cell structure of cellulose. NMMO effectively breaks the complex hydrogen bonds between cellulose chains and forms new hydrogen bonds between the hydroxyl groups of the cellulose and the NMMO molecules. This process creates single chain hydrogen bonds that are stabilized and dispersed into a homogeneous honey-like solution called, of course, “dope”. 

The solution is pumped through a spinneret with orifices like a shower head into an air gap where the cellulose molecules realign into strands, gaining their characteristically high strength. The now regenerated cellulose II is submerged into a water bath where the NMMO leaches out of the cellulose because of its higher affinity for water, allowing the new cellulose strands to coagulate and form solid fibers. After the coagulation bath, the cellulose fibers undergo further washing to remove any residual NMMO which is recycled and re-used in another dissolution process. The remaining material is Lyocell cellulose II fibers. These fibers are spun into yarns that can be woven or knitted into fabric.

Now, how is TENCEL™ different from generic Lyocell? TENCEL™ is a branded trademark of Lenzing AG - a fiber producer based in Austria. The TENCEL™ trademark now covers multiple fiber processes, but Athletic Articles underwear specifically uses TENCEL™ Lyocell. While the Lyocell process is relatively concrete, the individual components of the process are, as everything is, subject to varying levels of quality. TENCEL™ Lyocell maintains standards that are not guaranteed in the generic Lyocell process. 

From the beginning, the wood used as raw material for all TENCEL™ Lyocell fibers is sourced from controlled or certified origins meeting FSC® or PEFC standards. The production process uses a closed loop system where more than 99.8% of the dissolution solvent is recovered and fed back into the loop, resulting in close-to zero wastage. TENCEL™ fiber production has been certified to comply with modern quality, environmental, health and safety standards in accordance with ISO 9001:2015, ISO 14001:2015 and ISO 45001:2018. TENCEL™ fibers are certified with the EU Ecolabel for textile products in recognition of high environmental standards throughout their life cycle. And TENCEL™ products are certified to OEKO-TEX® STANDARD 100 class I under the strictest safety testing requirements for the presence of harmful substances. 

Apparel is one of the highest polluting industries in the world, and while brands are making an effort to limit their environmental impact, it isn’t enough to label products as “green” or “renewable” or “environmentally friendly” without providing evidence of how these efforts have been met. And until these efforts become standards, it will be up to the consumer to hold each brand accountable.