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What Is Cork And How To Turn It Into Fabric And Bags?

We are all familiar with cork stoppers, but what is cork made of, why is it eco-friendly, and how can it be turned into bags?

split image with on the left wine cork stoppers and on the right a cork shoulder bag from eKodoKi

When did cork start being used?

Going far back in time to 3000 BC, people like the Greeks, Egyptians, Romans and Chinese already appreciated the versatility and quality of cork. In fact, the ancient Greeks found that when the cork was removed from the cork oak, a new, better sheath quickly formed.

amphora with cork stopper which was used to contain wine or garum from North Africa

• In those times people already made cork stoppers for wine and olive oil vessels for their sealing quality.
Sandals were made out of cork because of the naturally shock absorbing quality.
Buoys and anchor ropes for fishing nets were made of cork due to their floating quality.
• The Romans even used cork to make beehives because of its low heat conduction.

Will there be a lack of cork?

Cork has been the one-size-fits-all closure solution for ages. It's only recently that it faces competition from alternative closures. There are many stories and myths going around about a supposably lack of cork and that the cork oak tree is endangered. And that they slowly are replacing the real cork of wine bottles with plastic corks or with aluminium screw cap instead for that reason. This whole story is a hoax.

a white wine bottle with aluminium screw cap and two white wine bottles with artificial cork stoppers all laying in ice cubes

The real reason of this cork replacement is that all other options are cheaper and that screw caps are more convenient. But be aware: an aluminium screw cap requires 24 times as many carbon emissions to produce as a natural cork. Moreover, there are enough cork trees today in the sustainable cork forests of Portugal to last for over 100 years. So there’s enough harvestable cork to seal all of the wine bottles produced in the world for the coming century.

Can cork be recycled?

Only natural cork and agglomerated cork (natural cork pieces that are bounded by an organic binder) can be recycled (not the waxed cork or granulated cork called DIAM, nor the obvious synthetic plastic cork). When natural cork is recycled it becomes a composite grain, a granulated material. Also waste during the production of cork stopper or the rejected corks are returned to the process and get recycled as well.

schematics of the cork recycling process from collecting old cork stoppers to agglomerated granulates other applications

There are recycling initiatives all over the world that specialise in recycling the natural wine corks through drop off points located in supermarkets, restaurants and bars. The collected corks are ground up and used to make goods such as footwear, yoga mats, surf gear, flooring and wall tiles and bulletin boards, etc.

NOTE: Both agglomerated and granulated cork can, by using moulds, be shaped in any form. Recycled cork from used cork stoppers cannot be used for new cork stoppers.

What is cork, really?

Cork is a natural raw impermeable buoyant material grown around the trunk of the cork oak tree, the phellem layer, which is the outermost layer of the tree bark. Cork is actually a conglomeration of dead cells.

Cork is a renewable resource. No tree is cut down to harvest cork, which means the tree keeps on living and the cork after every harvest regrows back.

cork layer detail from a cork oak tree bark

Cork material, in its natural form, is 100% natural and biodegradable. The lines running through them are called lenticels (small holes and splits in the cork) which are the gas exchange pores allowing air to get through the bark layer to the tree. The cork quality is determined by the number of these lenticels, the fewer the better.

Which layer of the oak tree contains cork?

photograph of a cork oak tree trunk section with all layers highlighted and numbered

1. Bark: consists of two layers, an outer dead layer (periderm, see 2) and an inner living layer (see 3 and 4).
2. Cork & cork cambium (phellem, phellogen and phelloderm / outer bark): non-functioning primary phloem (dead tissue) that protects the tree.
3. Living functional phloem (secondary phloem / inner bark): transports sugars produced by photosynthesis.
4. Vascular cambium (secondary phloem, and xylem / inner bark): produces new wood which increase the width of the stem.
5. Sapwood (early wood & late secondary wood, active xylem): transports water and minerals.
6. Heartwood (non-functioning primary wood, dead xylem): helps support the tree.
7. Pith

What kind of tree is growing cork?

The cork oak tree (in Latin: Quercus Suber) is a tree with a voluminous bark with suberose tissue (the cork). The cork oak is a majestic tree that has been around longer than mankind. Its presence in the world is believed to date back to about thirty million years ago.

cork oak tree with its bark harvested

Although related to the more common oak trees that are more worldly spread, cork oaks do not have the same typical oak leaf shape. They are oval, smooth and leathery. The cork oak has green foliage all year round, and can reach up to 10 to 15 meters in height when it is a matured tree.

The cork oak tree has a great longevity and an enormous capacity for regeneration. It takes 25 years before it starts to produce cork and lives ± 250 years.

Where does cork grow?

The agroforest areas are native to the western Mediterranean basin, most are in Portugal and Spain. The world's largest cork producer is Portugal, with a share of almost 50%, and around 28,000 people employed in the cork industry. Cork oaks can also grow in other places, but their produce is not always commercially suitable.

map of south west Europe and North Africa highlighting cork tree agroforests

• Portugal produces annually 100,000 Tons = 49.6%
• Spain produces annually 61,504 Tons = 30.5%

Due to reforestation programs, the areas of Montados have been increasing in the recent years. In Portugal and Spain over 130 thousand hectares were planted in the last 15 years.

What are Montados and Dehesas?

Cork oaks grow in agroforests called Montados in Portugal, or Dehesas in Spain. Both terms mean a multi-purpose agroforestry system with an open tree layer above a grass layer which depends on human practices and management.

cork oak forest slightly viewed from above

The cork oak forests achieved the Forest Stewardship Council (FSC) certification, recognizing that these forests and operations are managed to the highest international social and environmental standards.

These oak forests are large eco-systems, hotspots of biodiversity forming crucial habitats for various threatened animal and plant species and also preventing desertification. Over 200 species of animals like birds, reptile/amphibious, mammals etc. and 135 species of plants can be found in these agroforests.

How is cork harvested and does it kill the tree?

Harvesting of the bark is a manual ancient process executed by very experienced people called the “descortiçadores”, who do not harm nor kill the tree. Their razor sharp hand-forged iron axe is called “machada” (a broad hewing Viking type of axe) that is about a meter long with a wooden handle shaped into a wedge at the bottom. The axe form shape is like a ginkgo leaf.

descorticador using his machada to harvest the bark of a cork oak tree

First they make a vertical cut along the cork by choosing the deepest crack in the cork bark, this marks until where the cork plank should be removed and what is to remain on the tree. Then they open the bark and put the edge of the axe in the cut and by twisting it, it separates the outer from the inner bark. The bark is then prised of the tree, with the edge of the axe being put between the strip and the inner bark. Thereafter, the axe is twisted between the trunk and the cork strip to be extracted.

How often is an oak tree harvested?

Harvesting is only done between the end of May, beginning of June and end of August, when there is water in the tree and when the cells (phellogen) maintain their activity and continue to divide themselves.

The cork expands when the weather is warmer, which also makes harvesting easier. Only under these conditions can the cork be extracted from the tree without any damage.

detail of a numbered cork oak tree trunk with the bark recently harvested

After the cork is removed, the exposed tissue reveals a dark reddish brown color, and the tree gets marked by using the last number of that year. The cork bark will regrow, regenerate, to become harvested every 9 years. During its lifetime, a cork oak can produce, on average, 15 bark harvests.

When is cork harvested?

The cork quality of a tree changes over the years. The first harvest only happens when a tree is 25 years old and the trunk circumference is 70 cm. This “virgin” tree delivers a very irregular cork structure at start called “desbóia” a virgin cork that is hard and cannot be used for cork stoppers but is suitable for flooring or insulation.

split image with on the left the detail of a 25 year old cork oak tree bark and on the right the detail of a 43 year old cork old tree bark

Nine years later, the second harvest produces material with a more regular structure, less hard, but still not suitable for cork stoppers – this is known as ”secondary cork”. It is from the third harvest when the tree is around 43 years old and its following harvests after, that the cork has the best properties and is suitable to use for cork stoppers. This smoothest high end quality cork is called “Amadia”.

Why is cork harvesting a good thing to do?

By stripping the Cork oak tree from its cork bark the cork oak is able to absorb much higher levels of CO2 than before. A harvested cork trees absorbs 3-5 times more CO2 than non-harvested trees. It is estimated that every year cork oak forests absorb up to 14 million tonnes of CO2.

detail of a cork oak tree branch with the bark recently harvested

For every kilogram of cork produced, cork oaks absorb an average of 55 kilograms of CO2 from the atmosphere. They are sometimes even referred to as ‘The lungs of the Mediterranean’.

Why is cork stacked for long in the open air?

Once all the cork oak bark has been collected, the slabs are stacked on pallets and exposed to the open air for six months in the rain, wind and sun, which really improves its quality.

detail of slabs of cork oak tree barks stacked outdoor on palets

In general, the outside seasoned air and natural weather helps the bark to flatten, strengthen, and cure it.

How local vs global is the cork industry?

After the seasoned period, the cork bark is transported to factories for further processing. The vast majority of the cork harvest is made into wine bottle stoppers but, increasingly, more and more cork is being sold to construction and fashion industries all over the world. The world’s three biggest cork exporters are Portugal, Spain and France.

Although cork products like cork fabric are also still made primarily in Spain, Portugal, and France, other countries are increasingly making products based on cork.

slabs of cork oak tree barks stacked outdoor on palets in front of a cork factory

Sustainable materials such as cork also have disadvantages, of course. Since cork oaks can only grow under certain climatic conditions in the Mediterranean region, transport distances are longer than for the local extraction of wood. This in turn leads to an increased CO2 consumption. However thanks to the light weight quality of cork the impact is less than for heavy weight products.

Why does the cork bark need to be boiled?

The cork barks get boiled for at least 24 hours to soften them, clean them, to remove tannic acid and resins and to get them ready for further processing.

slabs of cork oak tree barks boiled in a cork factory

The boiling process increases the elasticity and the volume of the material, decreases its density, and functions as a natural fertilizer. After cooling down and drying for a second time, the cork is stabilizing for about two weeks to decrease its humidity to a degree that makes further processing possible.

How to cut cork into various usable pieces?

After stabilization, all the raw material of the cork bark is sliced by hand with a cleaver or by a cutting/sawing machine to obtain slabs of regular shape. On these first sliced slabs, the corks are cut out.

split image with on the left the raw material cork bark sliced by hand and the right sliced by electric saw

But for cork fabric, the cork pieces are cut in three layers and only the middle section, which is the densest and of the best quality, is used. The inner and outer layers are used for other products.

How is cork fabric made?

The middle layer itself is sliced again in layers of 0,3 to 0,4 mm like wood veneer to obtain the traditional look of textile. Occasionally, these slices have natural holes so that the applied backing fabric will shine through and becomes part of the look on purpose.

industrial cutting of 0,3 to 0,4 mm thin slices of cork to be used for the production of cork fabric

Sometimes they are coloured and cut into much smaller pieces for creating different agglomerated flocked patterns, and then glued into a block and sliced again. See for instance, eKodoKi’s bags made of “sienna flocked” cork pattern, like the KWORK Backpack M.

Gluing at this state can be done simply by applying heat. In most cases, no glue is needed, as the natural resin from the trees is strong enough to fulfil that function.

Optionally, PVA (polyvinyl acetate) is added, a water-based glue that is biodegradable and not contributing to the planet’s microplastics issue, as well as vegan (no animal derived ingredients used; no tests on animals).

How is cork fabric assembled?

arranging manually thin slices of cork for the production of cork fabric

The thin cork sheets are put in many possible sizes and patterns onto a backing fabric by hand. Without backing they will easily break. This requires a high precision skillset.

Is manufacturing cork fabric eco-friendly?

The thin cork sheets are laminated with a machine onto a fabric support backing bonded by suberin, a naturally occurring adhesive present in the cork to make it strong and to hold its shape.

industrial lamination of thin slices of cork onto a fabric backing to produce cork fabric

To ensure better adherence and higher stiffness, the aforementioned PVA
glue is applied between the backing fabric and the cork slices. Alternatively, a thermoplastic urethane film might be used in the lamination process.

Cork fabric is sometimes finished sanded and given an application of a protective finish. For the production of cork fabric, no heavy metals or their compounds, organic solvents, mineral fibres, or formaldehyde are used.

Is cork fabric available in many variants?

Cork is no longer a material of the past. With many new patterns and colours explored every day it is stimulating the creativity of designers, artists and architects who rediscover the beauty of cork.

There are many cork fabric variations – marbleized, striped, and flocked (agglomerated) – and natural cork has many natural tones that can be combined to have different effects.

patchwork of various cork fabric patterns

Cork fabric cannot be dyed like normal fabric; however it can be tinted (colour washed), or printed with any pattern in many colours with using water-based inks.

The material can be sewn or glued to other materials and surfaces, and embroidered. On top of that, it can be easily laser-cut and laser-engraved.

What are the qualities of cork fabric?

Cork fabric is 100% natural, durable, renewable, vegan, nontoxic and one of the most eco-friendly resources.

cork fabric close up

Warm and soft touch. Cork has an unique texture and pleasant luxurious touch.
No chemicals/toxins are used. Cork fabric can be produced without the harmful chemicals found in leather production.
Moister and stain resistant. Easy to maintain & clean: simply wipe clean with soap and water.
Long lasting & durable. Cork ages without it rots mainly thanks to its resistance to moisture.
Waterproof, fire resistant, and sound absorbing.
Lightweight (cork has a lot of air!); cork has therefore a floating quality.

What can be made from cork fabric?

Cork is no longer used only for the making of cork stoppers. It’s much more than that. Cork fabric has found its way in interior architecture, furniture, design, art, the fashion industry and even the automotive industry.

photomontage showing multiple applications of cork fabric such lamp shade umbrella upholstered armchair shoe and storage basket

A German company invented in 1890 an innovative solution for binding cork and rolling it into sheets, allowing it to be cut and used for any desired purpose. Following their example, creative people from all over the world in different disciplines have continued to design new ideas for making and using cork material in different ways, making it a popular material choice today and future.

Why is cork easy to sew and easy to cut?

Cork fabric has a similar handle to leather or vinyl, but it’s much easier to cut and sew with. Cork fabric is elastic and flexible due to its open cell structure called the phellogen. Every cell is a 3D shaped polyhedron, as small as 30–40 microns in diameter. One cubic centimetre of cork contains about 40 million cells, all filled with a gas similar to the atmosphere.

Cork is made up of more gas (90%) than solid material, making its density very low. Cork is therefore easy to sew and ideal for making bags. Not least because cork holds its shape well thanks to its cellular structure.

detail of a sewing machine presser foot stitching the border of a cork fabric piece plus insert showing cutting moulds and laser cutting

Techniques to cut cork fabric are:
CNC cutting – computer controlled cutting with blade
Laser cutting
Waterjet cutter
Steel moulds – the most traditional way for large product quantities.

Are cork fabric bags waterproof?

Despite having a spongy feel, cork fabric is waterproof and water repellent. If it wasn’t waterproof it wouldn’t make a very effective wine bottle stopper!

water droplets on a piece of cork fabric demonstrating its impermeability

Cork cells contain a fatty substance called suberin that helps it resist water absorption, making it ideal from everything from shoes to mobile phone covers. There are even umbrellas made of cork fabric. So even in countries where it often rains, there are no reasons not to opt for a cork bag!

Why is a cork bag a good choice?

Today, following the vegan movement, cork fabric bags are becoming popular alternatives to leather. But although cork fabric is then often referred to as “cork leather”, we prefer not to call it leather, as real leather comes from animals. Yet cork fabric is a great alternative to leather.

fashion model carrying a large cork shoulder bag from the brand eKodoKi

eKodoKi cork bags have a unique look and are innovative fashion statements. Cork is a gift from nature, for people who love environmental friendly materials and who care about nature and the future without compromising on quality or style. Not only is a cork bag light to carry, but it also has a durable quality for many years of use.

Photo credits

www.apcor.pt
• Close up cork bark
• Harvested cork oak tree
• Montado forest
• Harvest of cork oak
• Numbering cork oaks
• Harvest cork oak close up
• Cork Factory
• Cork cutting
• Cork fabric manufacturing

www.corkforest.org
• Stacked corkbark to dry

www.pixibay.com
• Cor on wooden table - dirkxili
• Winebottles in ice - SongOfSongs

www.eKodoKi.com
• Woman with eKodoKi cork & hanji bag
• eKodoKi cork & hanji bag collection

Icon credits

www.thenounproject.com
• amphora-3969186 – Adrien Coquet
• cork stopper-4059378 - Tyler Gobberdiel
• tree-rings-158730 – Kris Brauer
• tree-bark-1763789 – Lucas Helle
• leaf-1468646 – Saeful Muslim
• acorn-3351843 – Alena
• location-4436160 – Rizki Ahmad Fauzi
• deer-1568408 – Roundicons.com
• flying-bird-214911 – Agne Alesiute
• anole-lizard-3385835 – Pham Thanh Lôc
• trees-1878072 – Made
• axe-1408392 – Creaticca
• lungs-2177042 – Deemak Daksina
• co2 reduction-195841 – Carlos Dias
• pallet-308140 – Cono Studio
• truck-769073 – Nico Strobl
• factory-4428027 – SAM Designs
• steam-3267067 – Larea
• saw-4112766 – jonata hangga will putra march stanly
• fabric-3650460 – Llisole
• (structure) autocad hatch-1366900 – Liuia Iborra
• (structure) autocad hatch-1355455 – Liuia Iborra
• (structure) pentagon-202091 – Wes Breazell
• machine-1270908 – Eucalyp
• swatch-3414130 – Econceptive
• (durable) chain-2001018 – arif fauzi hakim

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