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The interior of a cork tree. The area harvested is in view, the a thick layer of outer bark contrasting with the lighter, interior bark.

Building Green

The Wonders of Cork as a Sustainable Material

Would it surprise you to learn that cork is a beautiful, sustainable material with many applications as an interior and exterior finish? This spring, Terry Phelan had the opportunity to witness a cork oak harvest firsthand and now shares the wonders of this product with you!

October 13, 2022

If you’re a designer, you’re probably familiar with the warmth of cork flooring and its ability to give rooms an acoustically desirable ambiance, as well as an elasticity underfoot not offered by other easy-to-clean hard surface floors. Cork wall panels also offer noise reduction in classrooms, music studios, and restaurants.

If you’re unfamiliar with cork, these benefits might be new to you! We love using cork in our projects.

There are many reasons we like using cork.

This past June, I had the good fortune to visit Portugal as a guest of Amorim Cork and Seattle’s Green Home Solutions to learn all about cork.

The exterior of the Amorim Showroom. The exterior is sided in cork tiles.
The Amorim Showroom

If you look closely, you can see the exterior of the Amorim Showroom is made up of large cork tiles.

We visited the Amorim manufacturing facilities and showroom in Porto along with a Port wine cellar, and then traveled to Lisbon to experience the harvesting operation in the cork forest.

What is Cork

Cork is an incredibly versatile and sustainable material that has many uses in building, finishes, fashion, and beyond. Cork comes from the cork oak, a tree with a very thick, spongy bark that is used to make different materials.

The outer layer of bark fall from a cork tree during harvesting. The outer bark in dark brown while the fresh, inner bark is a lighter color.
Cork Harvesting

Removing the outer layer of bark from mature trees doesn't harm the tree, making cork a renewable and sustainable material choice.

Cork oak can be grown and harvested in many regions, but the Mediterranean offers a bonus. After a tree grown in this region reaches thirty years of age, the outer bark can be carefully harvested every nine years with no harm to the tree.

This is due to a perfect combination of temperature, sunlight, moisture, and soil type. The harvest is limited to a mid-May to mid-July window to ensure trees have a chance to adapt while the temperatures are mild.

Why Cork is Such a Versatile Material

Cork has some unique characteristics that make it useful in many different applications.

The cell structure of cork is a closed polyhedron (basically a three-dimensional shape with flat faces, straight sides, and sharp corners), which makes it waterproof.

A close up view of the interior bark on a cork tree.
A Closer Look

Inside the outer layer of bark, the spongy and springy texture of the cork is visible.

These closed cells expand like popcorn when heated to a certain temperature and bind to each other with heat and pressure alone – eliminating the need to use adhesives. This process creates a highly insulative material that can be applied as sheets. And due to their waterproof nature, these sheets can even be used as an exterior finish surface.

Why We Love Cork

One of the oldest uses of cork is as stoppers for wine bottles – still the number one use today – but after the high-quality stoppers are punched out, the leftover cork granules can be put to many different uses. These range from insulation, flooring, shoes, and even fabrics, as well as composites for industrial applications.

A museum display of cork shoes.
Cork Shoes

Cork is such a versatile product – it can even be made into shoes!

The most familiar use of cork in architecture and interior applications is as a flooring material. Cork is a major ingredient in traditional linoleum, and both lino and thin cork tiles have been used for over 150 years.

Click floating cork flooring planks and wall coverings came on the market about 30 years ago, reinvigorating interest and use in homes and public spaces. More recently, cork insulation has been recognized as a natural alternative to rigid foam, and insulating cork siding has been used on some inspiring projects around the world.

Why Cork is Sustainable

Cork is considered a very sustainable material for several reasons.

  • It is completely natural and antimicrobial with no volatile organic compounds (VOCs).
  • Cork can be harvested while the tree continues to grow and sequester carbon.
  • It is so lightweight that shipping has a very low carbon footprint, and every granule can be captured and used. At Amorim, the last scraps are even burned to generate electricity!

Portugal is wonderful to visit at any time, and to be there during the annual cork harvest was a real treat. Going into the forest and seeing the skilled tree crew - many who were 3rd or 4th generation - ply their axes with such care and precision gave me hope that this process will continue well into the future. Now that’s sustainability!

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