I have seen some in Oman as well, it is not actual metallic thing(y) it is like a soft cardboard appears to be like metallic, which is a custom of some areas but nothing to do with the religion. I did not dare to ask the lady who was wearing this but I ask another lady who was not wearing this and she explained me, hope what she said was right.....else she was wrong and hence I'm wrong :)

Anil