Basically, anodised aluminium sheet consists of an aluminium core and an anodised exterior coating. The anodisation is created using a chemical/physical process. When looking at anodised aluminium sheet, we have a two layer material:
The aluminium core, which provides substance and stability while still being somewhat flexible.
The anodised layer on top, which is very thin (approx. 6-22 microns) but also very hard and strong, protecting the aluminium from chemical and physical influence.
The anodised coating itself is white in colour. Once applied, the anodised layer is coloured by embedding colour pigment in to the surface of the material, providing the final finish.