Cork comes from the outer bark of the cork oak tree, Quercus Suber, which grows mainly in the Mediterranean region. The bark is an agglomeration of cells filled with a gaseous mixture similar to air and lined with alternating layers of cellulose and suberin. Cork has remarkable properties that are unmatched by any other natural material which provides for an expanding range of practical applications.
Alexander the Great is reported to have been one of the many historic figures to have used cork. It is said that a piece of cork once saved him from drowning when crossing a turbulent river.
The Romans used cork in the construction of house roofs, beehives, ships and women's shoes.
In the 1600s, a French monk called Dom Pérignon took a giant step towards the modern, widespread use of cork as a stopper for bottles of wine.
In the late 1800’s cork powder was mixed with linseed oil, limestone and pigments to make natural linoleum.
In the 20th century, cork was the only organic substance to travel to Mars when it was used for thermal insulation in the Viking space probes.
Another widely used application of cork has been flooring in commercial buildings. Cork tile has been used in famous churches, galleries and pavilions worldwide such as: Sagrada Familia cathedral in Barcelona, the Serpentine Gallery Pavilion in London (2012), and the Portuguese pavilion in the World Exhibition of Shanghai (2010). It has also been used for decades in many university libraries (e.g. Ohio State Univ.), hospitals (e.g. Mayo Clinic) and local, state, and federal courtrooms. Other examples that are still going strong and look beautiful after 50 years are the Library of Congress, U.S. Department of Commerce Building in Washington DC, St. Mary of the Lake Chapel near Chicago, and Lafayette College in Easton, PA.
Today, cork has become even more popular with the development of eco-friendly residential and commercial flooring. Amorim has created a state-of-the-art water-proof flooring that is not only completely natural, durable and beautiful but emits no hazardous chemicals and is carbon negative. Due to its amazing properties, sustainability, and competitive pricing, cork has once again become a popular choice for flooring.
Cork oak forests cover approximately 2.5 million hectares across the Mediterranean region and most of them are located in seven countries: Portugal, Algeria, Spain, Morocco, France, Italy, and Tunisia.
The tree has a lifespan of 250-350 years. Each cork tree must be 20 to 25 years old before it can provide its first harvest of cork bark. This cork is known as virgin and has a hard and irregular structure. After the virgin cork has been stripped, a new layer of cork begins to grow.
The first of these layers, harvested after nine years, is called secondary cork; cork harvested after this second stripping is known by the Portuguese word: amadia.
A typical cork oak tree produces several hundred kilograms of cork at each harvesting and will survive for hundreds of years. Now, that’s sustainable! The bark is stripped off the tree in sections by skilled farmers using traditional axes, a manual skill that dates back many hundreds of years.
Cork is harvested every 8-9 years and the stripping of the bark does not harm the tree in any way. The bark grows back completely, taking on a smoother texture after each harvest. A cork oak tree can be safely harvested UP TO 20 TIMES during its life cycle, making cork a truly inexhaustible natural resource.
New plantations of cork oak trees are planted each year to ensure the level of cork production is maintained. Cork oak trees cannot be felled or removed without government authorization, which is rarely granted.
Portugal, which produces more than 50% of the world's cork, has been particularly careful to safeguard this valuable resource. The first Portuguese laws protecting cork oak trees date back to the 14th century. At the beginning of the 20th century, it became illegal to cut down cork oak trees, except for essential thinning or the removal of old, non-productive trees.
In a context of increasing concern for the environment, cork remains the only tree whose bark can regenerate itself after each harvest — leaving the tree unharmed. It is truly one of nature’s most renewable resources.
One cubic inch of cork is composed of no less than 200 million tightly enclosed air cells, each measuring l/1000" in diameter. Each minute cell is 14-sided, which virtually eliminates any empty space between the cells.
The bark of the cork oak tree has a unique honeycomb structure composed of tiny cells. Each cell has the form of a 14-sided polyhedron and the inner cell space is entirely filled with an air-like gaseous mixture.
Cork is light and floats on water. (Think fishing bobbers). That’s because about 89% of the tissue of the bark consists of gaseous matter. The buoyancy is derived from the low density and closed-cell structure with no open connections between each cell. You can think of cork like a closed-cell foam…although a natural one.
The presence of a waxy substance inside the cell walls known as suberin (a complex mixture of fatty acids and heavy organic alcohol) forms a gas and renders cork almost completely impermeable to both liquids and gasses. As a result, it is highly water-resistant and does not degrade or rot, making it one of the best seals available.
Cork has low thermal conductivity due to its structure of millions of small closed cells which eliminates convection. These impermeable compartments which contain suberin are insulated from one another by a moisture-resistant material. Radiation is also reduced through absorption and reflection of the numerous cell walls.
Cork consequently has a high level of thermal stability even at very high temperatures up to 2000° C which is why it is used in the space shuttle and as a fire retardant in buildings. Cork neither spreads flames nor releases toxic gasses during combustion which makes it an excellent fire retardant especially for buildings where many people work or congregate.
It has been said that cork has a great memory. The cell membranes of cork are highly flexible, making it both compressible and elastic which return to their original shape after being subjected to pressure.
These physical qualities allow the cork stopper to be fitted perfectly against the walls of the bottleneck. When it is subjected to strong pressure, the gas in the cells is compressed and considerably reduced in volume. When the pressure is released, and voila—the cork recovers its original shape and volume, showing no trace of having been subjected to any deformation.
Resiliency is measured mathematically in terms of compressibility. (Don’t worry, you will not be tested on this) Cork exhibits three levels of compressibility and this is important for those concerned about wear and tear and denting from heavy furniture or traffic on a cork floor.
The first phase of compression is from stress of 5-7% which bends the cells and is practically fully reversible. That means the natural structure will restore itself to its original shape. The second level of compression is about 50% where the cells begin to buckle. The final stage > 70% compression results in crushing of the cells. At this stage, the buckled cell walls touch each other and most of the suberin gas is exhausted.
What is unique about cork is that even after the last stage of high compression, the cell walls don’t fracture. In other words, the integrity of the material remains intact and the recovery of the original dimensions after the stress has been removed is rapid, resulting in the unfolding of the buckled cell walls. This is quite different from both hardwood and bamboo whose cell structure completely fails under heavy compression.
Furthermore, even if the stress comes from different angles, cork has the unique ability to undulate its cell walls which allows for large deformation without lateral expansion. While such stress may not be common in residential flooring applications, it’s good to know that extreme stresses (think kids skateboarding on your floor) won’t destroy your floor.
Finally, cork has a high friction coefficient which is tech talk for resistance to slippage and abrasion (on flooring). This makes for a more durable and long-lasting surface which explains, in part, why cork flooring owners say their floors have lasted for decades.
Cork is naturally antimicrobial and anit-fungal. Please read that sentence again. This characteristic is rarely talked about by industry or the scientific community. However, it is highly important, especially in light of the current environment of where viruses have plagued the world.
“Cork displayed high antibacterial activity against Staphylococcus aureus, with a bacterial reduction of almost 100% (96.3%) after 90 minutes of incubation, similar to the one obtained with ACA. A more reduced but time-constant antibacterial action was observed against Escherichia coli (36% reduction of the initial number of bacterial colonies).”
The summary stated: Portuguese cork displayed antibacterial activity against Gram-positive and Gram-negative bacteria, making this material suitable for several and extremely diverse industrial applications.
“Nowadays, synthetic materials are often used to replace products once made from natural materials, normally due to better properties and lower costs, although often with harmful effects to the environment, wildlife and human health. Furthermore, as these artificial materials are commonly nonbiodegradable, the chemicals used in their manufacture can leach out into the environment when discarded.”
Cork is also hypoallergenic because it is naturally anti-static and does not absorb dust. It helps protect against allergies and does not pose a risk to asthma sufferers. Cork flooring and wall coverings are also smooth and easy to clean making them less likely to harbor particles of dust or dust mites.
In these times of increased concern for our health and the health of our planet, the use of a natural product like cork for flooring comes at just the right time. Renewable, sustainable, biodegradable, antimicrobial, quiet, warm, safe, pure, comfortable, beautiful, climate positive and reasonably priced; it checks all the boxes. If you’ve never looked or walked on cork flooring, now is the time. Check out our selection of cork flooring products.