Where does a cotton T-shirt come from, and where does it go when it wears out?

In numbers

• ≈ 90%of cotton fibre is cellulose
• 6th millennium BCthe oldest known cotton thread

In five stops

1. 1

   Where were its atoms born?

   Cellulose is built from C₆H₁₀O₅ units: carbon, hydrogen and oxygen. The hydrogen comes from the Big Bang, the carbon and oxygen from stars. Your T-shirt's atoms share their origin with those of bread and sugar.

2. 2

   How did nature prepare it?

   The cotton plant makes glucose by photosynthesis and links thousands of glucose units into long chains of cellulose. The white fibres that grow around its seeds are made of this cellulose; in nature they help the seeds spread.

3. 3

   What did people do?

   The oldest known cotton thread was found at Mehrgarh in Pakistan, preserved inside copper beads from the 6th millennium BC. Today cotton is picked, a cotton gin separates the fibres from the seeds, and the fibres are spun into yarn, knitted into fabric, dyed and sewn. Cotton is the most widely used natural fibre in clothing.

4. 4

   What happens when we use it?

   Cotton absorbs moisture well, which is why it soaks up sweat. As it is worn and washed, the fibres slowly wear down and tiny bits of fibre are carried off in the wash water.

5. 5

   Where does it go next?

   A worn-out T-shirt can be worn second-hand, become a rag, or have its fibres separated and spun again. In soil, fungi and bacteria break down the cellulose and its carbon returns to the air as carbon dioxide. In airless landfills, rotting also releases methane, a powerful greenhouse gas.