How Is Cork Building Material Made? (Products to Make It)

A photograph of two cork building blocks. One is stacked on top of the other. The background to the image is a natural sheet of cork, and across the bottom are the words, "How Is Cork Building Material Made? (Products to Make It)." In the top right corner is the word "How?" in a handwriting font and underlined.

Cork is an eco-friendly building material with excellent air cushioning properties, which give it good sound insulation properties. Furthermore, because it contains 85% air, it is an excellent thermal insulator.

When used in walls, cork helps reduce heat loss by more than 30 percent. Such good thermal insulation characteristics are one of the key benefits of cork building materials.

But how is cork building material made?

Cork building material combines cork granulates with a granulometry ranging from 0.5 to 30 mm with a polyurethane formulation. The mixture is then treated at about 100°C (212°F) to agglomerate the building material, making it a composite for thermal and sound insulation.

In the rest of this article, I’ll discuss the combination of products that make cork building material. I’ll also discuss the factors affecting cork’s efficiency as a construction material.

Let’s get started!

The Combination of Products to Make Cork Building Material

Two photographs side by side. The left-hand photo shows the waste left over from the manufacture of wine bottle corks, and the one on the right shows a finished roll of cork flooring.
The manufacture of cork building products starts with the waste from wine bottle cork manufacture and ends with a beautiful product that is a good thermal and sound insulator.

Cork composites for building are made by combining cork granules, usually from the leftovers of wine cork making, with a polymeric binder and compressed under heat and pressure.

The resulting product is an extremely lightweight, fire-resistant material with excellent acoustic and thermal insulation.

The cork granulates used in this process account for 90-95 percent by weight. Polyurethane or phenol-formaldehyde resins come in as a binder to provide the required strength and stability.

The cork blocks obtained from this process are laminated, shaped into final dimensions, and finished for the intended purpose.

Besides its application in the construction industry, the material is also used as an anti-vibration shield in spacecraft due to its ability to absorb vibration energy.

The Properties of Cork Building Material

The increasing market pressure toward natural and sustainable construction explains the high demand for cork.

Cork insulation is becoming popular because the material possesses the following properties:

It’s Sustainable and Environmentally Conscious

A stack of freshly-harvested bark from cork oak trees.
Cork is harvested from cork oak trees once every 9-12 years and regrows without harming the trees.

Cork is a natural, renewable, and recyclable material with low embodied energy. It’s extracted from the outer bark of the cork oak tree.

The sustainability of this material is based on the fact that the tree doesn’t have to be cut. Instead, the tree’s suberin layer is stripped off, leaving the tree flourishing. Therefore, cork production doesn’t contribute to deforestation.

The renewability and recyclability of cork are based on the fact that cork oak trees regrow the suberin layer for fresh harvesting.

Cork is harvested every 9 to 12 years to allow the bark sufficient time to regrow and heal.

It Has Excellent Thermal Insulation

Let’s face it – energy costs are at an all-time high, and everyone is looking for ways to reduce their energy consumption.

As if that’s not enough, energy consumption contributes to environmental pollution as it involves burning fossil fuels. This process is responsible for 40 percent of man-made carbon dioxide in the U.S.

Insulation is a good way to reduce this problem.

A photograph of a roll of cork insulation with a roll of sticky tape on top. In the lower portion of the image are icons showing sound waves bounding off a soundproof surface and heat deflecting off a thermal insulation surface.
Cork is both a thermal insulator and a sound insulator.

Cork has excellent thermal insulation properties thanks to its numerous tiny air-filled cells. Since air is a poor thermal conductor, it increases the cork’s insulation capacity.

The presence of air-filled cells in cork explains why this material has a high R-value of 3.6 to 4.2 per inch. It also accounts for the material’s poor thermal conductivity, ranging from 0.036 to 0.38 W/mk. These features explain why Insulation Cork Boards (ICB) are a household name in envelope insulation.

Moreover, cork’s ability to withstand significant thermal variation, 292 to 248°F (144.44 to 120°C), makes it a suitable flooring material.

Finally, since cork is class 1 breathable, it retains indoor heat without trapping moisture, preventing mold and mildew formation.

Lightweight and Low Embodied Energy

Embodied energy is essential in determining the sustainability of building materials. A sustainable material must have a lower embodied energy than its alternatives.

Cork has very low embodied energy, making it the perfect choice for green construction.

The material’s lightweight nature is also an added advantage in terms of sustainability. Cork weighs between 10 and 15 pounds per cubic foot – more than ten times less than the weight of concrete.

Plus, the material is easy to install and transport, thanks to its lightweight nature. This feature reduces onsite labor and facilitates efficient transportation from the manufacturer to the construction site.

Hydrophobic and Impermeable

Suberin accounts for 40% of the cork used in construction. This component is highly hydrophobic and impermeable, meaning it repels water.

Cork’s impermeable nature explains why it’s a popular choice in flooring and roofing applications.

Moreover, its hydrophobic nature allows it to resist rotting due to moisture accumulation.

Excellent Acoustics

The spaces between the cork cells are primarily filled with air.

Air molecules are not in continuous contact with one another. Thus, they dissipate sound waves quickly, making cork a great soundproofing material.

This explains why cork is used in acoustic panels and floating floors. The material offers superior acoustics, absorbing up to 70 percent of external noise, thanks to its high noise reduction coefficient of 0.7.

Moreover, cork’s natural vibrancy helps absorb and attenuate sounds within a room. This feature makes it the perfect choice for music studios and other noisy spaces.

Fire Resistant

A photograph of a cork sheet with a diagram showing a red, yellow, and orange flame being deflected by the cork.
Cork contains suberin, which makes it fire-resistant.

Cork is highly fire-resistant, thanks to its suberin component.

Suberin increases cork’s ignition temperature to between 313 and 445°C (595.4 and 833°F). This feature makes cork an excellent fire retardant in construction.

Furthermore, the material is slow to burn and doesn’t release toxic fumes when exposed to fire.

This explains why ICB is an effective fire barrier in wall cavities, between floors, and other spaces where preventing the spread of fire is important.

The Impact of Density on Cork’s Thermophysical Value

Cork building material is analyzed based on its composition, thickness, and density.

Although thickness plays a significant role in the effectiveness of cork, the density of the specific species determines, to a great extent, the material’s thermophysical value.

According to research by CIGR Journal, low-density cork variants have low thermal conductivity and, consequently, excellent insulation. The table below shows these cork properties:

VariantThickness, cmAverage density, kg/m3Thermal conductivity, W/m-1/K-1

Table 1: Thermophysical values of cork. Source: CIGR Journal

So, How Is Cork Building Material Made? – Final Thoughts

Cork building material is an excellent choice in green construction.

The material is made from renewable resources and has excellent thermal insulation, soundproofing, fire retardant, and hydrophobic properties.

These features make cork an ideal option for those seeking to build an eco-friendly home or office.

A rule of thumb is to ensure your cork material is made from a high-density variant for excellent insulation.

As an eco-conscious homeowner or builder, check out these awesome examples of using sustainable construction for more inspiration.

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