Where Do the Differences Begin?

It all starts with the cork bark.

After harvesting, the pieces of bark are stored, sorted and processed according to their quality and intended use.

Not all cork bark has the same structure or quality. The age of the bark, harvesting cycle, pore structure and overall condition all influence how it can be used.

Suitable high-quality pieces of bark can, for example, be processed directly into natural cork products.

Other pieces of cork and suitable remnants from processing are broken down into smaller particles. This produces cork granules – an important raw material for many other cork products.

In simplified terms, the different processing routes are:

Cork bark → Natural cork

or

Cork bark → Granulation → Cork granules → Agglomerated cork

or

Cork bark → Cork granules → Thermal expansion → Expanded cork

Cork fabric is also based on natural cork. For this purpose, cork is processed into a very thin, flexible layer and bonded to a textile backing material.

Cork bark → Selection / Processing → Different cork materials

Natural Cork – Naturally Grown Cork Bark

Natural cork refers to cork in which the naturally grown structure of the cork bark remains largely intact.

The classic example is the natural cork stopper.

High-quality natural cork stoppers are made from suitable reproduction cork. The stoppers are punched directly from sufficiently thick, carefully selected pieces of cork bark.

This process preserves the material’s natural cellular structure.

Natural cork therefore does not have an artificially created granule structure. Pores, variations in colour and small irregularities are all part of the material’s natural appearance.

Typical Properties of Natural Cork

✔ Very lightweight
✔ Elastic with good shape recovery
✔ Water-repellent
✔ Naturally buoyant
✔ Thermally insulating
✔ Characteristic pores and grain
✔ Naturally grown cork structure remains largely intact

Natural cork has traditionally been used – and continues to be used – for bottle stoppers, floats, seals and numerous technical and decorative applications.

Cork Granules – Turning Cork into a New Raw Material

When cork is mechanically broken down, it becomes cork granules. Coarser fractions of shredded cork are also traditionally referred to as cork granulate or cork chips, depending on their size and application.

During this process, the continuous structure of the original cork bark is broken up. However, the characteristic cellular structure of cork remains intact within the individual cork particles.

This is an important distinction.

Cork granules are therefore far more than simply “cork dust”. They are a versatile raw material whose properties and applications depend greatly on the granule size.

Cork granules are used to produce, among other things:

✔ Agglomerated cork
✔ Cork rolls
✔ Cork sheets
✔ Moulded components
✔ Flooring and wall products
✔ Technical cork products
✔ Expanded cork
✔ Insulation and loose-fill materials

Suitable remnants from cork production can also be granulated and reused as raw material.

Cork granules therefore play an important role in making extensive use of the valuable harvested cork bark.

👉 Cork Granules – Sizes, Properties & Applications (coming soon)

Agglomerated Cork – Turning Cork Granules into a Versatile Material

Agglomerated cork – also known as composition cork – is made from cork granules and a binder.

Natural cork is first mechanically processed into granules. These granules are then mixed with a binder and processed under defined conditions into blocks, sheets, rolls or moulded components. After pressing and curing, the resulting cork material can be cut to size and further processed for a wide range of applications.

In our corresponding agglomerated cork products, the cork content is over 90%, while polyurethane resin (PU) is used as a binder at a proportion of less than 10%.

What Is the Binder?

Polyurethane resin is not a natural component of cork. It is a synthetic binder that permanently bonds the individual cork granules together and contributes to the strength, flexibility and durability of the finished agglomerated cork.

This is an important difference compared with natural cork and expanded cork: in agglomerated cork, an additional binder is deliberately added to the natural cork granules.

What Does This Mean for Material Quality?

The use of a binder does not automatically make cork an inferior or problematic material. What matters is the specific composition, the binder system used and the requirements of the intended application.

The corresponding agglomerated cork quality has also been tested by an independent laboratory for Substances of Very High Concern (SVHC) under REACH; the tested sample passed the test.

For food contact, however, it is important to note that polyurethane resins can have different formulations. Not every PU binder is automatically suitable for direct food contact. Any statement regarding food-contact compliance must therefore refer to the specific agglomerated cork quality and the relevant supporting documentation.

Fine or Coarse – Granule Size Makes a Difference

Different granule sizes are used depending on the intended product.

Fine-grained agglomerated cork has a more uniform surface and can be processed precisely for many applications.

Coarser granules create a more pronounced cork structure and, depending on the manufacturing process, may result in different mechanical properties.

However, granule size alone does not determine the quality of agglomerated cork. Density, bonding and the manufacturing process also play an important role.

This distinction is particularly relevant for cork sheets, technical components and flooring products.

👉 Agglomerated Cork – Production, Properties & Applications (coming soon)

Expanded Cork – Thermally Expanded Cork

Expanded cork is also made from cork granules, but its production process differs fundamentally from that of conventional agglomerated cork.

The granules are thermally treated at high temperatures. During this process, the cork material expands – its volume increases and its structure changes.

At the same time, naturally occurring components of the cork itself play an important role in bonding the individual granules together.

This process creates the characteristic dark brown to almost black expanded cork.

For this reason, Backkork is commonly referred to in English as expanded cork.

What Makes Expanded Cork Special?

✔ Made from cork granules
✔ Thermally expanded
✔ No additional synthetic binder required between the cork granules
✔ Characteristic dark colour
✔ Comparatively low density
✔ Good thermal insulation properties
✔ Good sound and vibration damping properties
✔ Frequently used as an insulation material

Our older specialist literature describes the manufacturing process as involving high processing temperatures. The exact parameters used in modern production may vary depending on the manufacturer and process.

We will therefore examine temperature, density and technical properties separately in our detailed guide to expanded cork, using current product and manufacturer data.

👉 Expanded Cork – Production & Properties (coming soon)

Natural Cork, Agglomerated Cork and Expanded Cork – Direct Comparison

Where Does Cork Fabric Fit In?

Cork fabric is a distinct form of processed cork and differs significantly from solid natural cork, agglomerated cork and expanded cork.

To produce cork fabric, natural cork is processed into very thin, flexible layers and bonded to a textile backing material.

The result is a material that combines the natural appearance and feel of cork with the flexibility and processing characteristics of a textile composite.

Depending on the specific type, cork fabric can be:

✔ Cut
✔ Sewn
✔ Glued
✔ Embossed or printed
✔ Processed into highly flexible products

Typical applications include:

✔ Bags
✔ Wallets
✔ Jewellery
✔ Accessories
✔ Clothing elements
✔ Cases and covers
✔ Decorative and creative applications

Our cork fabrics have a tear strength of 20 kg/3 cm according to ISO 13934-1. Elongation is at least 20% across the width and 15% along the length.

Cork fabric also performs well when exposed to moisture in everyday use. The material is water-repellent; bags and accessories can, for example, get wet during a rain shower and can simply be allowed to dry afterwards.

👉 Cork Fabric – Production, Properties & Applications (coming soon)

Which Type of Cork Is Right for Your Project?

The question cannot be answered simply by deciding which type of cork is generally “better”.

The intended application is what matters.

Important factors when choosing a cork material may include:

✔ Required material thickness
✔ Flexibility
✔ Density
✔ Granule size
✔ Thermal insulation
✔ Acoustic insulation
✔ Mechanical load
✔ Exposure to moisture
✔ Surface requirements
✔ Processing method

Fine-grained agglomerated cork may be ideal for one application, while expanded cork, natural cork, loose cork granules or flexible cork fabric may be much better suited to another.

👉 Which Type of Cork Is Right for Your Project?

What About Cork Rolls and Cork Sheets?

Cork rolls and many cork sheets generally belong to the family of agglomerated cork products.

Cork granules are bonded and processed to create flexible rolls or dimensionally stable sheets in different thicknesses.

Granule size, density, material thickness and composition can vary depending on the product.

This means that even within the category of agglomerated cork, different products are available for different applications.

👉 Cork Rolls – Which Thickness for Your Project?

👉 Cork Sheets – Thicknesses, Applications & Processing

What About Cork Insulation?

Different types of cork insulation also need to be distinguished.

Cork can be used, for example, as:

✔ Expanded cork insulation boards
✔ Cork granules or loose-fill insulation
✔ Insulating underlay
✔ Part of different floor, wall or ceiling constructions

Which solution is suitable depends on the particular construction and the required technical properties.

For building projects, the entire construction system as well as current technical and building-physics requirements must always be taken into account.

👉 Cork Insulation – Thermal Insulation, Sound & Applications (coming soon)

From the Tree to Different Cork Materials

Whether natural cork, agglomerated cork, expanded cork, cork granules or cork fabric – they all begin with the bark of the cork oak.

Cork Oak → Cork Bark → Selection and Processing

↓

Natural Cork

Cork Granules

Agglomerated Cork

Expanded Cork

Cork Fabric

This versatility is one of the reasons cork can be used in so many different areas – from bottle stoppers and flooring to insulation materials, technical components, bags and accessories.

Frequently Asked Questions About Natural Cork, Agglomerated Cork & Expanded Cork

Is agglomerated cork real cork?
Yes. Agglomerated cork consists predominantly of natural cork granules. In our agglomerated cork products, the cork content is over 90%. A binder is used to bond the individual cork granules together.

Is cork fabric made from real cork?
Yes. The visible surface of cork fabric is made from genuine natural cork, which is processed into a very thin, flexible cork layer and bonded to a textile backing. Cork fabric is therefore not solid natural cork, but a composite material with a natural cork surface. This combines the natural appearance and feel of cork with the flexibility and workability of a textile material.

What is the difference between natural cork and agglomerated cork?
In natural cork, the naturally grown structure of the cork bark remains largely intact. Agglomerated cork, on the other hand, is made from cork granules that are bonded together using a binder to form a cohesive material.

What is expanded cork?
Expanded cork is thermally expanded cork. Cork granules are treated at high temperatures, causing them to expand and bond together with the help of naturally occurring components of the cork itself, creating the characteristic dark material.

Does expanded cork contain adhesive?
In classic expanded cork, no additional synthetic binder is required to bond the cork granules together. Naturally occurring components of the cork itself perform an important bonding function during the thermal manufacturing process.

Why is expanded cork dark?
The characteristic dark brown to black colour develops during the thermal treatment and expansion of the cork granules. The high temperatures alter the cork material and create its distinctive dark colour. It is therefore not produced by subsequently colouring or dyeing the material, but develops naturally during the manufacturing process.

Are cork granules still real cork?
Yes. Cork granules are produced by mechanically breaking down cork. Although the continuous structure of the cork bark is lost, the characteristic cellular structure of cork remains within the individual granules.

Are cork stoppers always made from natural cork?
No. In addition to stoppers made directly from suitable natural cork bark, there are also stoppers made from cork granules or agglomerated cork. Their structure and manufacturing process vary depending on the intended application.