What makes cork a "sustainable" material? Is it how it's grown? How it's harvested? How it's manufactured? The answer is all of the above.
What is cork?
The cork material comes from the bark of the cork oak tree (Quercus suber), which is indigenous to the Mediterranean area - specifically Spain and Portugal. The bark undergoes a stripping process every 9-12 years, allowing enough time for the bark to fully regrow for its next strip. In addition to being a highly sustainable process, stripping prolongs the tree's lifetime - some have been recorded to be 500 years old, though on average they live to be around 200-300 years. Stripping also increases its carbon capture efficiency - the ability to capture and store carbon dioxide from the atmosphere.
Most of the cork that is produced is still used as wine corks, but what about the cork boards, flooring and trivets we see everywhere? That's called agglomerated cork - basically all the leftovers and grounded bits that get pressed together into new shapes and forms.
The manufacturing process
When superheated, for example with steam, cork releases a natural binding agent that allows agglomerated cork to be made easily and efficiently, without the use of additional synthetic chemicals.
Since cork comes from the bark and not the wood of cork oaks trees, it is naturally mold resistant, bug repellent, hydrophobic and fire resistant. This makes it perfect for things like insulation or flooring... or even planters!