Carbon-negative products explained.

How we calculate the carbon impact of products that use cork, including the ecosystem services of carbon-trapping cork oak forests.

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SOLE™ recently launched the first CO2negative™ Certified Carbon Negative footbed collection, made from ReCORK™ Recycled Cork. When something is carbon negative it removes more carbon from the atmosphere than it adds.

Everything we make has an impact on the planet. It takes energy to process raw materials, to power factories and to transport products. All of these energy requirements release greenhouse gasses into the atmosphere. 

So how can any product be carbon negative? The answer lies in properly accounting for the original source of our materials – living, breathing, carbon-trapping cork oak forests. 

We need to show exactly how much better cork is for the planet than materials made from fossil fuels. We need to quantify that difference in a way that tells the whole story.

Measuring a product’s carbon impact with a Life Cycle Analysis.

To accurately assess any product’s impact, it’s important to take a close look at all the small cumulative impacts that it has during its life cycle. To do this we commissioned a thorough, third-party life cycle analysis (LCA) of our footbeds. The LCA calculates the total combined impact of a SOLE footbed through every step of its life, from cradle to grave. 

This LCA was incredibly thorough, and rightly so. It took into account all relevant impacts including: raw material extraction, transporting materials, manufacturing, packaging, transporting products (to warehouses and customers), storing products, consumer care, and solid waste. 

Wondering what ‘consumer care’ of the product is? That’s the impact generated by heating your oven at home to 200°F for two minutes, to heat mold the footbeds; just one example of the LCA's thoroughness. We encourage you to read the full LCA.

The LCA report points out that an LCA is only as robust as the data that goes into it, and goes on to recommend that we continue to refine the data we use as an input, in order to increase precision. Since the LCA report was published, we have attained more accurate primary data in certain input cases. Using the LCA calculator provided to us, we have thus further refined the cradle-to-grave impacts shown by the LCA. 

carbon negative insoles made with recycled cork

The carbon impacts of the Active Thick and Performance Thick footbeds.

Two LCA results for two different footbeds.

The Active Thick has an overall impact of 2.42kg CO2e per footbed, while the LCA calculator for the Performance Thick shows an impact of 1.94kg CO2e per pair. We'll get to how we calculate a carbon negative impact for the Performance Thick soon, but first: why the different LCA outcomes?

The only difference between the Active and Performance footbeds is the material that makes up the base of each. While the Active Thick is made from petroleum-based EVA, the Performance Thick is made from natural cork. The cork in the footbed itself contains carbon that has been absorbed from the atmosphere as the cork grew on the tree. The result is that the raw material impact of the Performance Thick is 0.304kg CO2e compared to the 0.7776kg CO2e of the Active thick. This explains the difference in the LCA assessment of the two footbeds.

While the carbon impact numbers for Performance footbeds are significantly lower than the non-cork equivalent, they're still carbon positive numbers. So how do can we claim that the Performance collection is carbon negative, with the Performance Thick having a carbon impact of -2.2kg CO2e? The answer lies in looking at the bigger picture, and properly accounting for the role played by living cork oak forests.

a graph showing how we calculate carbon negative climate impact

Accounting for the ecosystem services of cork oak forests.

Cork comes from the bark of carbon-trapping cork oak trees. In ideal conditions, for every kilogram of cork produced, cork oak forests absorb up to 70kg of CO2 from the atmosphere. This carbon sequestration is referred to as ‘ecosystem services’ of the cork oak forest. 

Standard LCA methodology stops short of accounting for those ecosystem services, but we believe this fails to fully show the positive impact of using natural cork. To accurately account for the overall impact of using cork, we calculate the CO2 absorbed by cork oak forests to produce the cork we use, on a per-weight basis. We then include that carbon sequestration in a final calculation to get to our final impact number for cork products.

To ensure we are not over-calculating the CO2 sequestered we do not use the ‘ideal conditions’ figure of 70x the weight of cork used. Instead we use a more conservative evaluation of 55x the weight of cork used, which is the average CO2 uptake in cork oak forests. This is in line with the methodology of cork industry leaders and experts. 

That initial calculation of carbon absorbed, per weight of cork used, gives us a deeply carbon negative starting point. We then add to that number the total carbon footprint of the product as determined by its cradle-to-grave LCA. In the case of the Performance footbed collection, the result is a an overall carbon-negative impact. The carbon absorbed by cork oak forests to grow the cork we used is almost double the total emissions of the product's lifecycle.

Why do we account for the ecosystem services of cork oaks when standard LCA methodology does not?

We believe that it’s crucial to recognize and account for the impacts on the planet of every choice and decision we make. When faced with a choice between cork and petroleum-based foams it is not sufficient to say ‘using cork is better for the planet than petroleum-foams’.  We need to show exactly how much better cork is for the planet than materials made from fossil fuels. We need to quantify that difference in a way that tells the whole story. 

It’s our firm belief that human society has an imperative need to recognize the full value of resources that present effective solutions to the climate crisis. Few such resources exist;  cork oak forests are one. By accounting for the impact of those forests in our calculations, we place a numeric value on the benefit of choosing this sustainable resource. 

the climate impact of soles footbeds as shown by co2e labelling