The material is silicon
NSN 5998-01-490-1815
NSN 5985-00-983-1050
NSN 5925-01-272-0894
NSN 6150-01-392-3327
NSN 6220-01-227-0907
NSN 5960-01-342-9965
NSN 5910-01-105-0546
NSN 6240-00-705-7731
NSN 5905-01-089-8438
NSN 5855-00-631-4565
NSN 5925-00-290-4451
NSN 5935-01-573-6696