Cross-section of cork bark.

Cork bark has many amazing properties.

Image: Thinkstock

Written by Sarah Kellett

Bottles of champagne may send corks sky high, but spacecraft take cork as far as Mars. Their success depends on it.

Cork reached new heights as part of the protective aeroshell that insulated the Mars rovers Spirit, Opportunity and Curiosity from the intense heat of entering the Martian atmosphere.

Bark of the cork oak tree contains a waxy chemical called suberin. This chemical contributes to making cork bark elastic, buoyant, waterproof and fire resistant.

Unlike most trees, cork oaks regrow their bark after it is cut off, making it a sustainable natural product. Bark can be harvested every ten years or so after the tree is about 30 years old.

The structure of cork resembles honeycomb filled with gas, and one cube of cork a centimetre on each side can contain 40 million air cells. Compressing and expanding, these tiny pockets of gas make cork strong, but with enough give to make it a comfortable option for flooring and shoes.

As the bark provides insulation to the Mars rovers, so it does on the tree. Fire resistant qualities allow cork oaks to survive wildfire better than many other trees.

Harvesting can leave cork oaks more vulnerable to fires, according to a study by a European team of researchers. They found the thicker the bark, the better a cork oak survived fire. Trees with bark thicker than four centimetres were unlikely to die from heat injury.

Protecting cork oak trees from fires, Mars rovers from heat, and champagne from spoiling, cork is truly one useful bark.

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