There is no Space for Cork…

Cork. Lately I regularly come across publications and buildings with Cork. Ideal insulator, it seems, and weatherproof, And quite a decorative material, recently saw some nice applications in construction design. Well, that could be so, but is it a serious option? For that, we have to dive into some figures.

From the time the cork oak is about 25 years old, the bark can be peeled every 9 years. The first 2 harvests produce poorer quality, then it’s good: only the 3rd harvest, after about 50 years, is suitable for something other than pellets. That is real planting for the future… After the bark is peeled its processed into cork products. And it takes another 9 years before the bark is thick enough for new cork to be harvested. From a cork oak tree that is 80 years old, you can harvest 40-60 kg of cork, and the average cork oak lives about 200 years, producing about a ton of raw cork over its lifetime. That would be 65,000 bottle corks. (And 70% of all cork goes into wine tops…)

There are about 2,200,000 hectares of cork forest worldwide (33% in Portugal and 23% in Spain). Annual production is about 340,000 tons. That leads to yields of about 150 kg/ha-year averaged over the years. [1][2][3] [4]

Using a different route to control, we get approximately the same result: A brief analysis via google shows that , when zooming in, there are about 40-60 oaks per hectare, with about 50 kg of cork per 9 years per oak, (and no harvest in the first 25 years), so that approximately corresponds to 150 kg/ha-year as well, averaged over the life span.

The cork oak forests also provide work: it takes 4.7 man-days to harvest 1 ton of bark, and another 3.5 man-days to maintain the forests per ton of cork harvested, making a total of 8.2 man-days/ton. Per harvest round (once in 9 years) per hectare 500 x 50 kg is 2.5 tons, results in 16.5 mandays. Or roughly 2 mandays per hectare per year. So that’s pretty low.

But so is the yield per hectare-year indescribably low: 150 kg/ha-year. It’s more than sheep’s wool (.) [5] , but still. By comparison, forest growth yields roughly 5-10 m3 of wood per hectare, at about 5-600 kg dried per m3, , or between 3 to 5000 kg of wood per ha-year, and potatoes yield even up to 40,000 kg/ha-year [6]) Thus, cork is absolutely not a material that you can or want to use widely, and thus should not promote its use.

By the way, the embodied energy of cork processing is quite low at 4 MJ/kg, so if you only look at the product ( good properties and organic) and the embodied energy, it all looks great.

But it should be required to always include the land use, when cork is mentioned. By the way , the embodied energy can also be expressed in land use : in m2 of solar radiation converted into electricity , or in biofuel , or diesel, via rapeseed for instance. And this way everything can be and is related to land use, in a society based on renewable resources. I describe that in my recent (Dutch) book and I will come back to that here. [7] [8]

An occasional building with cork is no problem of course, but if you look globally and want to apply cork, it is disastrous. So use cork, like so many materials, only where the requested properties can only be fulfilled by cork, and by no other material. Materials are not bad or good, it’s how you use them. And Cork should not ne used, and is not needed in construction, the bulk demand is too great and there are alternatives enough.

Problem is you can’t blame someone for applying cork. Such a person usually does not have the overview and does not see the consequences , if that product is used 1 million times or 1 billion times globally.

Therefore, actually, we would need an authority that looks globally at whether a product can be permitted to enter the market: If the product if purchased by everyone in the world far exceeds the system capacity, it will not be licensed/authorized for production. But it might take be some time before we have an international “bullshit products authority…

So for the time being, don’t apply cork yourself, professionally speaking.

PS: and for wine caps you should do a separate analysis again, compared to plastic caps or screw caps. Or yet back to refillable bottles via the barrel at the winery….

[1] wiki en


[3] Portugal which produces roughly half the world’s cork (310,00 tons from 2,150,000 hectares).

[4] production proces (without impacts) :

[5] wool:

[6] potatoes:

[7] book Post fossil Life: in dutch, later this year in English: Post Fossiel Leven:

[8] landbudgetting :

Author: ronald rovers