Special Materials vs the Undead

Alchemical Silver: Bypasses the damage reduction of creatures such as lycanthropes but does not have the properties of true silver vs the undead
Amber: Bypasses the damage reduction of creatures whose soul is suspended in the horrors of undeath such as Ghosts.
Celestrial Mithral: Bypasses the damage reduction of creatures such as lycanthropes as well as most shadow based undead such as wraiths and shadows. Counts as Silver for purposes of vulnerability and regeneration.
Cold Iron: Bypasses the damage reduction of creatures such as some Fey specific undead such as Bansidhe
Jade: Bypasses the damage reduction of extraplanar creatures such as Demons and Shadows
Mithral: Bypasses the damage reduction of creatures such as lycanthropes as well as most shadow based undead such as wraiths and shadows. Counts as Silver for purposes of vulnerability
Silver: Bypasses the damage reduction of creatures such as lycanthropes as well as most shadow based undead such as wraiths and shadows
Silversheen: Bypasses the damage reduction of creatures such as lycanthropes but does not have the properties of true silver vs the undead.
Turquoise: Bypasses the damage reduction of creatures such as Hags

Special Materials vs the Undead

Annwyn: Dreams of Winter Lost Nightfalcon