Cotton wool as an insulator is often made of natural cotton as well as cotton recycled from waste and cuts of clothing. It is therefore a green material. It is better to choose recycled cotton wool, the conventional cultivation of cotton being very polluting. It is both a thermal and sound insulator.

Cotton wool comes in rolls, felt and plates, but its use as felt is mainly for sound insulation. This insulator can be used for walls, roofs and floors. Cotton wool is treated against fungi, xylophages and dust mites and it can be treated with boron salt to make it fire resistant. It is a good hygrometric controller as it is very permeable to water vapor.

Cotton wool is relatively expensive (more than hemp and wood wools) but recycled wool offers the best prices.