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May be a French helmet, I had a very similar one not too long ago, same construction style but early nylon. I believe this is a type of liner for a hard shell helmet. Very hard to say without more photos, markings, etc. You can spend hours looking unless able to narrow it down a little.
Hi,
My wife is Czech and the zip yon your helmet is very common one used through the 1940's - 1950's in the old Czechoslovakia, so this might help you date it, I have bags of these zip at home.