One of the London auction houses thought that it could be an eighteenth century fireman's helmet or possibly a seventeenth century inner lining for a Cavalier's hat .
I don't think it's either. The leather firemen's helmets that I've been able to find have been much cruder and utilitarian than this. They also have flaps that hang from the back to protect the neck.
As for being something worn under a hat; I don't think so. It's too well made, and the decorative leather work implies that it was meant to be seen. Also, if I was a Cavalier, I'd be wearing a metal inner helmet, not a leather one. And why have a rim designed to keep rain off the face if it's worn under something else?
The only things that I have seen like this (although in metal) are kettle hats. They seem to very often have this decorative strip running from front to back. And I have seen this wavy line design. Did they make a variation in leather? Perhaps for archers? I have read accounts of archers having to take off their metal kettle hats, when discharging their arrows, because the metal brims got in the way. Maybe a (very hard) leather helmet with a narrow brim was a compromise for someone.
I have shown it to an expert in textiles who has confirmed that it has been very well made. She was very impressed with the uniformity of the stitching. She also can't see any reason why it couldn't be Tudor, or even earlier.
Any ideas?

