Invisible Mail

A variation of the Armor spell, this spell enables the caster to cover his body with an invisible suit of plate mail to temporarily raise his AC to 3. Its effects are not cumulative with other armor or magical protection (a character cannot improve his AC better than 3 through use of this spell), but Dexterity bonuses still apply.
For each level of the caster, the invisible mail absorbs 1 hit point of damage that would normally hit AC 3; however, the invisible mail offers no protection against magical weapons or attacks. When the invisible mail has absorbed as many hit points of damage as the wizard has levels of experience, the invisible mail disappears. The invisible mail does not hinder movement, nor does it add weight or encumbrance. It does not interfere with spell casting.
Example: A wizard with a normal AC of 10 has shielded himself with invisible mail. The first opponent attacks with a normal dagger; the attack is made against the AC 3 of the invisible mail. The attack is successful, causing 2 hit points of damage, but this damage is absorbed by the invisible mail and the wizard is unharmed. A second attack is made with a sword +1, The invisible armor offers no protection against this magical weapon, so the attack is made against the wizard's normal AC of 10.

[Complete Wizard's Handbook]

School: Evocation, Abjuration
Level: 3
Rarity: Uncommon

Range: 0
Components: V, S, M
Duration: Special
Casting Time: 2
Area of Effect: The caster
Saving Throw: None

Material Components:
a small fragment of plate mail