This little piece started as a quick note in response to this post, but snowballed into a full-on essay on cellulose-based fabrics. Read on or save for later but do yourself a favour: stay informed!

The basics

Let’s start with the basics, to make sure we’re all on the same page.
Here’s a definition of sustainable: “the quality of not being harmful to the environment or depleting natural resources, and thereby supporting long-term ecological balance”. 

Now, the post starts with a joyful shout: “Modal: trendy & sustainable”, which annoyed me a great deal.
I usually keep my mouth shut as I am very aware I still know too little about these topics to butt in, but this was so obviously “green bait” and I just couldn’t hold it. I did 10 minutes (I promise) of research and learnt a whole lotta stuff that I feel like sharing so, here you go. 

Production is only one side of the story

Let’s start with Modal.

Modal is a partially synthetic fabric, just like viscose rayon. The raw material used for production is wood, which cut and chipped into a pulp and then squished into thin spaghetti that make up the fibres used to weave the fabric. There are several steps of going from wood to fabric that should be taken into account when evaluating overall sustainability:

  • sourcing of raw materials,
  • production waste and processing of the fibre,
  • production and dying of the resulting fabric
  • usage and disposal of the finished item of clothing

It’s extremely difficult to evaluate any given piece of clothing, as the variables in this layered chain of production are extremely complex and often vary manufacturer to manufacturer and equally largely on usage.  So, for the purpose of making this blog post readable, I’m going to stick to the usual point of conversation when discussing rayon & co.: fibre production. 

Let’s start with looking at what needs to happen to make Modal fibre. Here’s an image from Sewport that will help: 

So first we need to harvest the wood (the sustainability conversation on this specific part of the whole process is just as complex, but as I said I will leave it out for brevity’s sake).
Then the wood is broken into chips from which we need to extract cellulose (it’s worth noting that trees only contain 40%-50% of cellulose whereas cotton, for instance, is made of 90% cellulose) by steeping the chips into a solution of caustic agents (caustic soda and sodium sulfide). The resulting pulp is then “marinated” into carbon disulfide to create cellulose xanthate, a stretchy substance that is pressed through what looks a lot like a very fine cheese grater, to make xanathe “spaghetti”. These are then spun and subsequently treated with sulfuric acid to reconvert the Cellulose Xanathe into regular cellulose.

Finally, the cellulose fibres are stretched and dried and eventually ready to be made into fabric. 

Thus simplified, the process to make Modal and to make old-fashioned Rayon (aka viscose) is exactly the same. 

However, Modal, due to slight changes in the conditions in which this process is executed, produces much stronger and longer fibres which result in less piling and a longer life span of the final fabric.

(Where) Are we throwing the baby and the bathwater?

A consequence of the production process of cellulose-based fibres is a huge amount of highly toxic chemical waste.

Carbon disulfide by itself is a potent neurotoxin harmful to both humans in direct contact with it (the workers) and the environment it is dumped into. I couldn’t find much on what traces of it are left in the finished fibres, but personally I wouldn’t assume that there aren’t just because there isn’t info avaialble.

Now, back into production for a sec: this is where specific set up of manufacturing make all the difference when it comes to sustainability.

There are three main issues:
1. the sourcing of the raw materials 
2. whether it’s an open or closed production loop
3. disposal of wastewater

Once again, I’ll skip point 1. as it’s a whole new topic I’m not yet prepared to explore. 

So fast forward to point 2, aka Production loop: an open production cycle is when all the materials (chemical and organic) used for the process are brand new and whatever is left over is tossed away as waste – usually dunked into a stream of water.

A closed-loop, instead, can be obtained is steps are taken so that all or part of the waste can be re-used. A fully closed loop would see no waste whatsoever. (To nobody’s surprise often partially looped production systems are falsely advertised as fully closed.)

There are many producers of cellulose-based fabrics, everywhere in the world, and each one of them has their own processes and working standards.
It would be impossible to trace them all and list them down. One that is very worth mentioning though is Lenzing, Austrian producer of Rayon, Modal, Lyocell and Tencel.

Lyocell & Tencel

I’ve already quickly mentioned the difference between Rayon and Modal (the length and strength of the fibres).

Let’s talk about their hipster siblings: Lyocell and Tencel. 

Lyocell looks very similar to Modal and Rayon, but is made in a slightly but significantly different way.

Enters NMMO, aka N-Methylmorpholine N-oxide! 

The NMMO is used in the production process not only to replace the use of caustic soda in extracting cellulose from the wood pulp but also allows to skip entirely the carbon disulfide step, as the resultant cellulose can be simply dunked in water to “solidify” it into fibres.

Further brownie points: NMMO is easier to collect and re-use, thus allowing to create a fully closed loop! Now we’re getting closer to talk about something that looks vaguely environmentally friendly.

Finally, Tencel. This is Lenzing’s (the austrian company) own trademark on a Lyocell based on a 100% closed NMMO production process that only uses Eucalyptus trees from sustainably managed forests.
The idea is that Eucalyptus (similarly to bamboo) grows super fast and with much less water than birch trees usually harvested to make the fibres. 


Let’s go back for a sec to the block post that sparked my outrage and curiosity.

Is Modal environmentally sustainable? Heck no. 

Is it better than Viscose: yes, because the fibres are nicer and could potentially last longer. Potentially being the key word here. 

Are cellulose-fibres more sustainable than cotton/wool/synthetics?: totally debatable and relative to the specifics of the production process used.

I would personally argue that a recycled fabric (be it natural or synthetic) is more sustainable than any other fibre that is created with raw materials. However, this is just a skip, hop and jump from saying than the most sustainable fabric is the one already in your stash (big shout to Orsola De Castro here). 

Like most of you, I have more questions than answers. But that does not and should not stop any of us by politely calling companies out on abusing “sustainability” in their marketing messaging.

In my opinion, it is too important a subject nowadays to muddle the waters with wafer-thin justifications as to why one chooses to call Modal “sustainable” (you can check my original comment and the company’s* response in the original post, linked to the first picture). Modal, however a brutal a chemical process, is a beautiful fabric to wear and that’s all that can be said about it.

Lastly (I swear), please please please do not forget that this is only one slice of the conversation. We haven’t even touched on the dying process of the fibers (which traditionally is even more polluting than producing the damn fibers). There are new processes and technologies discovered every day that can radically alter the logic illustrated in this slap-dash piece on cellulose-based fibres so, keep reading and KEEP QUESTIONING.

Further reading and sources:

Wikipedia: Rayon, NMMO, Derivatization, Lyocell

*It’s not my intention to discredit or isolate this particular company. I want to pinpoint a cheap-ass, videly diffused and otrageously abused practice of word-smithing “marketing bait” for busy people who don’t always have the time or energy to question what they read and might end up believing into what is essentially greenwashing.


Add yours

  1. Well done for taking the time to research and explain. This isn’t the first time I’ve heard of the spurious claims about this material but I wasn’t familiar with the term ‘green bait’. And I was feeling a dress coming along this weekend (since it’s been a while that I’ve made anything) and planning to shop for some fabric but I’ll take the advice that the most sustainable fabric is the one already in your stash .

    Liked by 1 person

  2. Thank you for such a thoughtful and informative post. I’ve pretty much given up buying new fabric- I use my stash and thrifted fabric and repurposed fabric. Having said that, I cannot abide polyester and have eliminated it from my stash. I don’t believe it’s good for the body or the environment as the lint is so bad. I even avoid polyester thread these days. I hope you continue to explore this interesting topic.

    Liked by 1 person

    1. Thank you! I think every material has its purpose, but we have definitely abused plastic & derivates (aka polyester) to generate single-use commodity clothing that in the end pleases nobody. I can’t say I’m as well behaved as you are, but awareness goes a long way in helping with forming good habits. Will keep sharing what I find! Thanks for reading 🙂

      Liked by 1 person

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