Kovar is an iron-nickel-cobalt, controlled expansion alloy with 29% Nickel, 17% Cobalt, and the remaining balance Iron. Kovar expansion characteristics match both borosilicate (Pyrex) glasses and alumina ceramics making it one of the most popular of the controlled expansion alloys for hermetic sealing applications allowing direct mechanical connections over a range of temperatures in conductors entering glass envelopes of electronic parts. It is also known as ASTM F-15, NILO K, Pernifer 2918, and Dilver P1.