Cork

Cork has some impressive qualities, unmatched by manmade materials. Once dried, it is lightweight, impermeable to liquids and gases, highly compressible and resilient. It provides excellent thermal and acoustic insulation, is a fire retardant, and highly abrasion-resistant.

Its unique mix of ingredients and honeycomb cellular structure give it perhaps its most magical quality – it has a Poisson’s ratio close to zero. This means that when squashed it resists expanding sideways, and is why it is so satisfying to cork a bottle. Most solid materials have a positive Poisson’s ratio, because they thin out as they are stretched and expand sideways as they are squashed. A rubber stopper, for example, would jam in the neck as it’s pressed.

The job of cork on the cork oak (Quercus Suber L.) is to provide protection – it is waterproof, antimicrobial and antifungal – all good qualities that can be utilised in products made of this material. Cork exists on all trees as a thin protective layer just below the bark. Only on the cork oak does it grow thick enough to be harvested and converted into products and packaging. It is native to the western Mediterranean region (Portugal produces around 50% of global production). The bark is harvested every nine years, without felling or harming the tree.

Stopper production produces waste in the form of granules. They are used to make agglomerate, which is converted into sheet, moulded and extruded products. Several other novel applications have emerged, which attempt to take advantage of all the benefits of cork, such as providing an impact absorbing base layer in artificial grass pitches (instead of rubber), mixing granules with concrete to produce a structural material with improved noise dampening, and combining granules with plastic to produce a biocomposite suitable for sports products, footwear and furniture.