Grades 3–5 · Materials & Matter
Why is cork so light and springy?
Cork comes from the outer bark of a cork oak. A small piece feels surprisingly light because much of its volume consists of tiny gas-filled cells. Thin walls separate these enclosed spaces.
In the diagramGas-filled cells change shape under a pushBeforeCompressedAfter releaseEnlarged gas-filled cells; recovery has practical limits.
The cell walls make a framework around the gas rather than filling the entire piece with dense solid material. This structure lowers the piece’s overall density. It helps explain why ordinary cork can float on water.
When cork is pressed, its cell structure can change shape and the enclosed gas can compress. After the force is removed, much of the structure can recover. That recovery gives cork its useful springy feel.
The small closed spaces also hinder heat transfer through the material. The same microscopic arrangement therefore contributes to lightness, cushioning and insulation. A cork board and a stopper use different shapes of material with related internal features.
About this explanation
Starting knowledge: Know that a material can contain spaces much smaller than the eye can see.
Sources
- Corticeira Amorim — What is cork?
- Corticeira Amorim — Key characteristics of cork