It's made of "papier maché" as we call it. In English it's called fiber board I think... A mix of paper fibers and glue... The neck guard seems to be vulcan fiber...
I have one in my collection and it was not easy to find it...
Also one strange thing is that the plate that should hold the spike on the inside of the helmet is on the outside. That looks also period done on this haube... I also have one helmet that's assembeled this way...
Imo this still is an interesting and hard to find helmet...
I asked him for info along those lines and the seller never replied. I don't like when that happens much... makes me feel as if there is something he's hiding....