Last making Course 101.
The Last, in footwear making, is the model to which the footwear is moulded around. It remains inside the footwear during the making process.
Most lasts, for upscale bespoke, begin as a last blank. This blank is established with heel height, toe spring and cone build into it. The custom footwear maker begins to shape and model the last to fit the individual according to measurements and style ordered by the customer.
These last blanks, are mechanically turned. For the more technically advance firms, cad/cam software is used to design and turn the lasts. They can be modeled from both plastic and wood. The most common bespoke lasts are wood perhaps because it is the easiest to shape and polish. It is traditional.
Plastic being a more stable medium is best if your customer will have changes in their feet during a particular day and you want to last to remain the size you made it to be.