What is ironing, anyway? It is the reshaping of textile fabric from wrinkled to smooth. Simple enough on the surface, quite interesting when you look closely: The heat of the iron loosens the connection between the molecule-chains in the fibres. The pressure of the soleplate then reshapes the fabric, and when it cools down, the connections between the molecule-chains rebuild. So what was a stubborn crease is now smooth and will stay that way (until it is worn and washed again…).