Very little is known about the strange substance known as protodermis. The Matoran of Onu-Koro have been mining it for many years as a source of energy, but even they are uncertain of what it is or where it comes from.
After a huge underground battle, the Toa fell into large tubes filled with protodermis. They returned to the surface with new armour, new tools and new powers. The Toa are now more powerful than ever. This is why they have given themselves a new name: Toa Nuva.
Source: The Official Guide to BIONICLE