What is the difference between virgin, agglomerated and carbonised cork?

1. Virgin cork, also called natural cork

Cut from the harvested plank with the original cell structure preserved. This is the most expensive form and the one people picture when they think of cork. It is used for wine stoppers and high-end pieces where the natural grain is the point.

One nuance if you work in wine. In the strict trade sense, virgin bark is the FIRST stripping from a tree of about 25 years, and it is rough, so it goes to rustic pieces and to granulate. Stopper-grade cork comes from the later reproduction harvests. Outside the wine trade, virgin cork simply means unprocessed natural cork, and that is how it is used here.

2. Agglomerated cork, also called composite or white cork

Cork granules mixed with a binder and moulded under heat, between about 110 and 150 degrees. Coasters, table mats, decorative sheet, tiles, wall panels, yoga mats and gaskets are almost always this.

The reason it dominates is that it is tunable. Granule size, binder and ratio can all be adjusted, so the same material can be made denser, finer or more flexible depending on what it has to do. The Regular and Premium finishes on our coasters are exactly this: the same cork, a different granule size.

It is worth knowing that agglomerated cork is not purely natural. The binder is a synthetic resin. That matters for two real questions, cleaning and food contact, and it is why saying cork is natural does not answer either of them on its own.

3. Carbonised cork, also called expanded, black cork or ICB

Granules are treated in an autoclave with superheated steam, at around 300 to 350 degrees. The cork expands and its own resin binds it together, so there is no added adhesive at all. It comes out darker, which is where black cork comes from.

This is an insulation board, used for thermal and acoustic work. It is not a decorative surface and it is not what a coaster is made of.

It is also the answer when a project cannot accept an added binder, because there is not one. If that is a requirement on your specification, say so early and we will talk about carbonised cork rather than agglomerated.

Which one you are buying from us

Nearly everything in the Green Haven range is agglomerated cork, form two. If a piece is virgin or carbonised cork we will say so, because the difference changes the price, the look and what the piece is good for.

It also changes the customs classification, which matters on an export document. Note that customs uses the term NATURAL cork rather than virgin: articles of natural cork and articles of agglomerated cork sit under different headings, and getting that wrong on a shipping bill is a real problem rather than a technicality.

What is agglomerated cork?

Cork granules mixed with a binder and moulded under heat at about 110 to 150 degrees. Also called composite or white cork. It is what most cork products are made of, including coasters, table mats, tiles, wall panels and yoga mats, and its properties can be tuned by changing granule size, binder and ratio.

Is agglomerated cork natural?

The cork is, the binder is not. Agglomerated cork is cork granules held together with a synthetic resin. That distinction matters for cleaning and for food contact, because those questions are really about the binder rather than the cork.

What is carbonised cork?

Cork granules treated in an autoclave with superheated steam at around 300 to 350 degrees, so the cork expands and its own natural resin binds it with no added adhesive. Also called expanded cork, black cork or ICB. It is used as thermal and acoustic insulation board, not as a decorative surface.

What is virgin cork?

Cork cut straight from the harvested plank with its original cell structure intact, also called natural cork. It is the form used for wine stoppers and high-end pieces. In the wine trade specifically, virgin bark means the first stripping from a young tree, which is rougher; stopper-grade cork comes from later harvests.

Which type of cork are Green Haven products made from?

Nearly all of them are agglomerated cork. Where a product is virgin or carbonised cork we say so, because the form changes the price, the appearance and what the piece is suited to.