Expanded cork was developed in the mid 1990s to provide a 100% natural insulation material, using parts of the cork bark that were not previously used. When the cork oak tree is stripped of its bark, generally only the trunk is stripped and the upper branches are left untouched. The cork bark from the upper branches cannot be used to make natural corks, as it is not thick or uniform enough and contains too much resin.
However this upper branch cork can now be used to make expanded cork, which makes use of the naturally occurring resins to bind granules under pressure without using any additional adhesives. Once this cork has been stripped from the tree, it is made into granules, which are placed in a mould and compressed. Then super-heated steam is added to reach temperatures of up to 370ºc for 20 to 30 minutes, which causes the resin held within the cork granules to come to the surface. this resin now becomes the adhesive that binds the granules together – meanwhile, the heat also causes the granules to expand. What is left is a block of expanded or black cork, which can then be cut into boards of varying thickness (generally 10mm to 300mm) with a density of between 105 and 125 Kg/m3.
This expanded cork is much darker that normal cork because of the resins and it also has a distinctive resinous odour that fades over time. As well as being 100% natural and recyclable, expanded cork is a fantastic insulation material as the expanded cells contain 50% air and are also waterproof and fireproof.
The technical characteristics of expanded cork are:
Thermal conductivity coefficient – 0.040 W/m.K
Density – 105-125 Kg/m3 (7.0 – 7.5 pounds per cubic foot)
Tension to stress – 1.4-2.0 KGf/cm2
Functional temperature range – -180ºc to +140ºc
Fire class – Euroclass E
R value – 3.6 per inch
Compressive strength – 15 psi
Moisture permeability – 2.2 perms at 40mm
The main applications are for exterior walls or double walls for acoustic and thermal insulation, but it can also be used under paving slabs (for noise reduction) and for thermal and acoustic wooden panels and a range of other insulation applications. Please contact us if you require any further information or would like a quotation.