Bronze face mask, plated with silver sheet? The bowl of the helmet appears to be made of iron, once covered with a layer of bronze sheet, now much corroded.
The rear portion may very possibly have been covered with animal hair originally, on top of the bronze sheeting.
The rear part of the helmet is virtually the same as a 'normal' cavalry helmet of the 'Weiler' type.
References:
Junkelmann, M, (1996), "Reiter wie Statuen aus Erz", p.28, Abb.44 & p.93
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