I never knew an iron hat like that existed. Its like making a baseball cap out of kevlar
It's a 'sercret' on steroids. Many wore an iron secret (effectively an armoured skull cap) underneath a 'normal' hat. This is the same, but slightly more integral to the hat. There's one on display at the West Berkshire Museum in Newbury.
Zoom in to clearly see the metal liner. The hat is on display the wrong way round, the nose guard is missing but it is possible to see the whole, and the bracket that allowed it to be raised and lowered at the back of the hat (as displayed).