The material is silicon
NSN 5835-00-389-2816
NSN 5998-00-290-1829
NSN 6685-00-374-0482
NSN 6240-01-030-3794
NSN 5905-00-825-3614
NSN 5905-00-918-1466
NSN 6685-01-467-8789
NSN 5930-01-187-6236
NSN 6620-00-699-5537
NSN 5965-01-526-3190
NSN 6610-00-868-4838
NSN 6105-01-383-6534