Suberin – turns bark into tires and shoes

If you examine trees and plants closely, a world of molecules and chemicals is revealed, and an exciting new world of opportunities. The trees in the forest are no exception. The most common substance to extract on a large scale is cellulose. The part of the wood pile that is most interesting, however, is the outer bark – especially from birch. 

This is a translation of an article signed Torbjörn Johnsen at

Log Max Harvester Heads
It’s the outer bark of the birch that contains suberin. Photo: Torbjörn Johnsen

Suberin – turns bark into tires and shoes

The Swedish start-up company Reselo has entered a journey to exploit one of those substances: Suberin. A substance that, among other things, can replace fossil rubber in tires and shoes. 

We visited Reselo in its research lab close to Stockholm. We met the product manager Josefin Larsson who guided us through the possibilities of exploiting suberin from birch bark, a substance that is a residue from the pulp industry. A residue that today is used as fuel for energy production. 

The outer bark of birch contains several interesting substances. Approx. 30 – 40 percent of it, is suberin which could be described as something like cork. Another substance in the birch bark is betulin. Also, this substance is interesting to exploit as a replacement for many fossil-based substances. 

The suberin’s characteristics make it suitable to use as different kinds of rubber-like polymers. As mentioned above, it can replace the rubber in e.g., tires and shoes. The World Market for rubber is approx. 30 million tons annually of which two-thirds are tires. Approx. 2 million tons are used for shoes. To replace all of this with suberin-based materials is not possible but especially the shoe market is interesting as it is an end-user market. Reselo is already in negotiations with a “major shoe manufacturer” who is interested in sustainable rubber. 

From birch bark to suberin, a material that could be used for rubber manufacturing. Photo:

EU financing and start-up money

So far, Reselo is in the early stage of development. You can say that the company works on two parallel tracks of which the first, process development, is made with EU financing. That means developing the process to extract the suberin from the bark and reach the level of an industrial process. 

In the Reselo lab, the extraction process is developed and the manufacturing of different types of materials is tested. Photo: Torbjörn Johnsen

The other track is about product development and finding out which types of polymers and materials could be replaced by suberin-based materials. Materials that can match the customer’s demands. 

For this part of development, the company has raised start-up capital that should take it from an innovation lab to the market. This journey contains finding industry partners who can develop an industrial application for suberin exploitation. 

A sheet of rubber-like material made from suberin. Samples have been taken from the sheet to examine the characteristics in the Reselo lab. Photo: Torbjörn Johnsen

Yet another leg for the pulp industry? 

What kind of companies could make suberin? Looking at companies that handle vast volumes of birch bark you come to think of the birch pulp mills. A handful of companies in Sweden have pulp mills for birch and they could take on this challenge if they want to. The situation in Finland is similar. 

Reselo doesn’t reveal exactly what discussions are underway but confirms that they are in contact with several companies in this matter. Sweden and/or Finland are realistic as bases for manufacturing suberin according to Reselo. 

Free bark?

An alternative to getting birch bark in large volumes could be to debark the pulpwood in the forest before it’s sent to the pulp mill. This could give the forest owners an extra assortment to make money on. An assortment that the forest owner today doesn’t get paid for as the pulpwood is measured under the bark. 

Unfortunately, today’s measurement regulations don’t allow such a solution (in Sweden and Finland). The pulpwood must be delivered with the bark on it even though the forest owners only get paid for the wood. 

Larger interest from the customers

According to Josefin Larsson, the interest so far is larger among the customers where several validation projects are underway. As for production, Reselo has dialogues with several pulp mills about the benefits of processing birch bark and the potential of Reselo Rubber. The benefits could be seen both from a business- and a sustainability perspective. 

Reselo already has managed to get birch bark for the development lab. When we visited Reselo, a cubic meter of bark was lying on the floor for drying in a meeting room. From this pile, the researchers will pick out the outer bark and through a chemical process extract suberin. 

A cubic meter of birch bark for drying in a meeting room. Photo: Torbjörn Johnsen


There are no official calculations for the economy of suberin production, but the substance as such has a large value. According to Reselo, the value of traditional fossil-based polymers for rubber production is below 5000 USD per metric ton. For “non-fossil” material, the prices should be higher. 

A homemade “quick-and-dirty” calculation shows that a large pulp mill, that handles a million cubic meters of birch pulpwood annually, should be able to make 10000 – 15000 tons of suberin annually. The market value of that is approx. 50 million US Dollars. And in addition to that, the substance betulin could be extracted from the birch bark. If this is possible parallel to the suberin extraction is however unclear, and so is the issue of patent protection, etc. 

But it’s interesting – there is money to be made in the new “bio-economy” if you start extracting substances with far higher values than the traditional cellulose pulp and the “lignin fire”. 

As we see it, the end customers will be the driving force in the development of this and not the potential producers. Trend-setting shoe manufacturers who work with their sustainability image are first in line to get non-fossil rubber for their shoes ASAP. 


Reselo is still a start-up company, and its timeframe suggests that the work with process development should be done by 2024. The next step will be to do trials together with selected/interested partners. After that, the goal is to, in cooperation with a producer, get a semi-commercial demo plant up and running. One that can produce some thousand tons of suberin annually and from thereon move on to more and larger plants. 

A realistic scenario, according to Josefin Larsson, is that there will be a profitable, large-scale manufacturing process running in five to ten years’ time. 

Read more about Reselo on their home page here

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