Hardness

A character with Hardness X reduced all non-magical, non-adamantine physical damage by X. Magical and non-adamantine damage is reduced by half of X. Hardness is not applied to adamantine, force, disintegration, or any damage listed as a weakness.

Robots are typically weak to electricity. Non-combat robots have hardness of 5. Medium combat robots have a hardness of 10. Larger robots can have more.

Undead-constructs are typically weak to positive energy.