Agglomerated Cork – Production, Properties & Applications
How Cork Granules Become a Versatile Material
Agglomerated cork – also known as composition cork – combines the natural cellular structure of cork with the possibilities of modern material manufacturing.
The raw material is cork granules. The individual cork particles are bonded together using a binder and processed under defined conditions into blocks, sheets, rolls or moulded components.
This makes it possible to produce cork materials with different thicknesses, granule sizes, densities and surface structures.
In the corresponding agglomerated cork qualities we offer, the cork content is over 90%. Polyurethane resin (PU) is used as the binder at a proportion of less than 10%.
👉 Natural Cork, Agglomerated Cork & Expanded Cork – What’s the Difference?
What Is Agglomerated Cork?
Agglomerated cork is made from cork granules that are bonded together with a binder to form a cohesive material.
This fundamentally distinguishes agglomerated cork from solid natural cork: the original cork bark is first broken down into granules. However, the characteristic microscopic cellular structure of cork remains intact within the individual granules.
As a result, agglomerated cork retains many of the typical properties of the natural material.
At the same time, the manufacturing process makes it possible to specifically influence properties such as granule size, density, strength, flexibility, material thickness and surface structure.
💡 Good to Know
Agglomerated cork is real cork – but it is not pure natural cork.
The majority of the material consists of natural cork granules. An additional binder permanently bonds the individual cork granules together.
In the corresponding agglomerated cork qualities we offer, the cork content is over 90%.
How Is Agglomerated Cork Produced?
The production of agglomerated cork begins with natural cork. Suitable pieces of cork and usable remnants from cork processing are broken down and then processed into a new cork material.
In simplified terms, the production process can be represented as follows:
Cork or suitable cork remnants → Granulation → Cork granules → Sorting by granule size → Binder → Shaping & Pressing → Curing → Further Processing
1. Cork Is Processed into Granules
Suitable pieces of cork and usable remnants from cork processing are mechanically broken down.
This produces cork granules, which can then be sorted according to different granule sizes and qualities.
Granule size is an important factor in the subsequent manufacturing process, as different sizes of cork granules can be used depending on the desired product.
This creates a versatile natural raw material that can be specifically processed into a wide range of cork materials.
2. The Granules Are Mixed with a Binder
To turn the individual cork granules into a stable, cohesive material, a binder is added.
For the corresponding agglomerated cork products we offer, polyurethane resin (PU) is used for this purpose.
Polyurethane is not a natural component of cork, but an additional synthetic binder. Its function is to permanently bond the individual cork granules together.
It is therefore important to make a clear distinction:
Cork granules = natural raw material
PU resin = additional synthetic binder
In the corresponding agglomerated cork qualities we offer, the cork content is over 90%, while the proportion of PU binder is less than 10%.
3. Shaping and Pressing
The prepared mixture of cork granules and binder is then shaped and pressed according to the desired product.
This process can produce cork blocks or other moulded forms, which can be further processed after curing.
Granule size, compression, binder and manufacturing process make it possible to produce agglomerated cork materials with different densities, thicknesses, strengths and surface structures.
As a result, agglomerated cork can have very different properties depending on how it is manufactured.
4. Curing and Further Processing
After shaping and pressing, the material must cure to form a permanently stable bond.
The resulting cork blocks or moulded components can then be further processed depending on the desired end product – for example by cutting, sanding or other machining methods.
Agglomerated cork is used to produce, among other things:
✔ Cork sheets
✔ Cork rolls
✔ Underlays
✔ Moulded components
✔ Flooring products
✔ Technical cork products
✔ Decorative elements
Why Does Agglomerated Cork Need a Binder?
When cork bark is broken down into granules, the continuous structure of the original piece of bark is lost, leaving individual cork particles.
To bond these particles together again into a dimensionally stable, cohesive material, an additional binder is used in the production of agglomerated cork.
The type and proportion of binder – together with cork quality, granule size, density, compression and manufacturing process – are among the factors that influence the properties of the finished agglomerated cork.
An important distinction should also be made between agglomerated cork and expanded cork:
Agglomerated cork: Cork granules are bonded together using an additional binder.
Expanded cork: Cork granules are thermally expanded; in classic expanded cork, no additional synthetic binder is required to bond the cork granules together.
👉 Natural Cork, Agglomerated Cork & Expanded Cork – What’s the Difference?
💡 Good to Know
Agglomerated cork is real cork – but it is not pure natural cork.
The majority of the material consists of natural cork granules. The additional binder permanently bonds the individual cork granules together to form a new material.
In the corresponding agglomerated cork qualities we offer, the cork content is over 90%.
Fine or Coarse – Why Granule Size Matters
Agglomerated cork can be produced using cork granules of different sizes.
The granule size primarily influences the appearance and surface structure of the finished material and can also affect some of its mechanical properties.
Fine-Grained Agglomerated Cork
Fine cork granules create a comparatively smooth and uniform surface.
This can be advantageous, for example, when:
✔ Precise cutting is required
✔ A finer surface is preferred
✔ Smaller components are being produced
✔ A uniform appearance is important
Coarse-Grained Agglomerated Cork
Larger cork granules remain more visible and create a more pronounced cork structure.
Depending on the manufacturing process and density, the mechanical behaviour of the material may also differ.
The important point is:
Finer does not automatically mean better – and coarser does not automatically mean lower quality.
The right granule size depends on the intended application.
Density – An Important Technical Parameter
Alongside granule size, density is an important technical parameter of agglomerated cork.
In simple terms, it describes how much mass of a material is contained within a given volume.
Agglomerated cork products can have different densities even when they belong to the same general material category. Density is influenced by factors such as granule size, compression, binder content and manufacturing process.
Density can, in turn, affect various properties of the finished agglomerated cork, including:
✔ Strength
✔ Compression behaviour
✔ Recovery behaviour
✔ Weight
✔ Flexibility
✔ Thermal and acoustic insulation properties
A higher density does not automatically mean higher quality. What matters is which properties are required for the intended application.
The actual density therefore depends on the specific agglomerated cork quality.
An example with technical values for one of our documented agglomerated cork qualities can be found in the following table..
Technical Data for One of Our Agglomerated Cork Qualities
The following technical specifications are available for one of our documented agglomerated cork qualities:
| Property | Specified Value |
|---|---|
| Cork granules | 3–7 mm |
| Density | 230–300 kg/m³ |
| Tensile strength | ≥ 400 kPa |
| Compressibility | 10–30% |
| Recovery | ≥ 65% |
| Resistance to boiling water | No disaggregation |
Tensile strength describes, in simplified terms, the tensile stress the material can withstand.
Compressibility describes how much the agglomerated cork can be compressed under a defined pressure load.
Recovery indicates the extent to which the material returns towards its original shape after the load is removed.
The specified resistance to boiling water with no disaggregation means that, under the conditions of the relevant test, the tested material quality did not break down into its individual cork granules.
This explicitly does not mean that every agglomerated cork product is permanently waterproof.
💡 Good to Know
Technical values always apply to the specific agglomerated cork quality being tested.
Properties such as density, tensile strength, compressibility and recovery depend on factors including granule size, compression, binder and manufacturing process. They therefore cannot be applied universally to every type of agglomerated cork.
Compressibility and recovery are closely related: agglomerated cork can be compressed under a defined load. Once the load is removed, the material has the ability to recover towards its original shape.
The extent of this behaviour depends on the specific agglomerated cork quality. The characteristic elastic cellular structure of the cork within the individual granules continues to play an important role.
Cutting and Working with Agglomerated Cork
The most suitable tool depends primarily on the material thickness and density.
For thinner cork materials, a sharp knife or scissors may be sufficient, depending on the product.
For thicker agglomerated cork sheets, saws are often the better choice.
It is always important to use a sharp tool so that the granulated structure can be cut as cleanly as possible and the edges do not crumble or break unnecessarily.
👉 How to Cut Cork Sheets Properly
👉 How to Cut Cork Rolls Properly
How to Glue Agglomerated Cork
Agglomerated cork can be bonded to many suitable substrates.
Important factors include:
✔ Substrate
✔ Material thickness
✔ Mechanical load
✔ Surface area
✔ Moisture exposure
✔ Adhesive used
For many of our applications involving cork sheets and cork rolls, we use or recommend WAKOL D 3540.
With this contact adhesive, the adhesive is applied to both surfaces to be bonded. After allowing the adhesive to flash off, the surfaces are brought together, creating an immediate strong bond.
🛠 Workshop Tip from korkie
Agglomerated cork is easy to work with – provided that the tool and material thickness are well matched.
With thinner materials, a clean cut can often be achieved without difficulty. For thicker cork sheets, a suitable saw will usually provide cleaner and more controlled cut edges.
Before starting a larger project, we also recommend testing the adhesive, tool and desired result on a leftover piece of cork first.
Agglomerated Cork, Natural Cork or Expanded Cork?
All three materials share the same natural origin, but differ significantly in the way they are produced.
Natural Cork
The naturally grown structure of the cork bark remains largely intact.
Agglomerated Cork
Cork granules are bonded together using an additional binder.
Expanded Cork
Cork granules are thermally expanded and bond together without the need for an additional synthetic binder between the granules.
👉 Natural Cork, Agglomerated Cork & Expanded Cork – What’s the Difference?
🌿 Conclusion – Agglomerated Cork Makes Cork Highly Versatile
Agglomerated cork combines a high proportion of natural cork with the possibilities offered by a technically manufactured material.
The cork bark is broken down into granules, which can then be bonded with a binder and processed into sheets, rolls, blocks and moulded components.
Within the individual granules, the characteristic cellular structure of cork remains intact.
However, granule size, density, binder and manufacturing process all play an important role in determining the properties of the finished agglomerated cork product.
The key point is:
Not all agglomerated cork is the same.
The right material should therefore always be selected according to the specific application.
Frequently Asked Questions About Agglomerated Cork
Is agglomerated cork real cork?
Yes. Agglomerated cork consists predominantly of natural cork granules. In the corresponding agglomerated cork qualities we offer, the cork content is over 90%.What is the difference between agglomerated cork and natural cork?
In natural cork, the naturally grown structure of the cork bark remains largely intact. Agglomerated cork is made from cork granules that are bonded together with a binder to create a new material.What binder is used for agglomerated cork?
In the corresponding agglomerated cork products we offer, polyurethane resin (PU) is used. Other agglomerated cork products may use different binder systems depending on the manufacturer and intended application.Is polyurethane natural?
No. Polyurethane is a synthetic material and is not a natural component of cork.Is agglomerated cork food-safe?
This cannot be answered in general terms. Some cork agglomerates use binders suitable for food contact, for example in certain cork stoppers. Whether a specific agglomerated cork product is suitable for direct food contact must be confirmed by the relevant product quality and supporting documentation.Is agglomerated cork water-resistant?
Depending on its quality, agglomerated cork can have good resistance to moisture. However, this does not automatically mean that every agglomerated cork product is waterproof. The binder, density, surface treatment and duration of exposure all play an important role.What does granule size mean in agglomerated cork?
Granule size refers to the size of the cork particles used. It primarily influences the appearance and surface structure and, together with density, binder and manufacturing process, can also affect the properties of the finished agglomerated cork.A finer granule size does not automatically mean higher quality. The intended application is what matters.
Why is density important in agglomerated cork?
Density describes how much mass of a material is contained within a given volume. In agglomerated cork, it is related to properties such as strength, compression behaviour, weight and flexibility.A higher density does not automatically mean higher quality. What matters is which properties are required for the intended application.
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Any Questions About Cork?
Would you like to use agglomerated cork for a project, or are you unsure which granule size, material thickness or specification is best suited to your application?
With over 30 years of experience working with cork, we are happy to provide personal advice to help you choose the right material and offer practical guidance on processing and suitable applications.
Our Service for You
✔ Personal expert advice on agglomerated cork
✔ Support in choosing the right granule size and material thickness
✔ Advice on cork rolls and cork sheets
✔ Practical know-how on processing and applications
✔ Personal customer service by phone or email