Coco is made using the outer husk of the coconut shell. It's naturally rich in potassium and sodium, so most coco products are pre-treated by the manufactures so that they are ready to use. Coco fibre has been found over many years to be an effective growth medium that produces big, healthy plants and prolific harvests.
Coco is a relatively light medium that has good water retention without becoming soggy: it is much harder to over water coco than soil. It has an excellent air capacity of around 30% which aids root growth and nutrient uptake.
Coco contains a naturally occurring fungus called Trichoderma that helps prevent disease and aids root development. Due to gradual leaching of potassium from the coco it is strongly advised to use a coco-specific nutrient.