See photos as they are a part of this description

Liner appears to be molded plastic similar to a hard hat material. It is stamped SW-71 inside 

I personally don't know anything about the liner but in my investigation it could be foreign military issue

This may be an early example of an Austrian M58 liner, I found another example with SW 71 stamped but it had 9-10-11-12-13 around the stamp. This one is only 9-10-11 around the main stamp.