The visor, which allowed the face-plate of the helmet to be raised away from the face in battle when not in danger, was very new in 1314. It was used only by those who could afford the very latest designs, so it would not have been worn by many knights at Bannockburn.
The face-plate was cut with ‘sights’ which allowed the wearer to see out of the helmet, while holes called ‘breaths’ made it easier to breathe.
The visor helped to deal with a number of helmet issues. In the raised position it allowed the helmet to work open-faced, so that a knight could see, breathe and communicate more easily.
However a wound to the eyes or face could easily kill you, so the visor also allowed you to be protected – an important new development.