Higher tier materials resist damage better, but each material tier 1 and up has a weakness (which is parenthesized in the list). Weapons in which material is weak against treat that material as being one tier lower.
Tier 2 and tier 3 materials obsolete all materials of lower tiers.
Glass (Glass is Tier 0.3 against lasers but is tier 0 against all other damage.)
Cupronickel (weak to Railgun)
Iron Copper (weak to Missile)
Iron-Nickel (weak to Laser)
Copper Gold (weak to Railgun)
Ferrotitan (weak to Missile)
Nickel Gold (weak to Laser)
Titanium Gold (weak to Railgun)
Titanium Copper (weak to Missile)
Nitinol (weak to Laser)