An invisible but tangible field of force surrounds the subject of a mage armor spell, providing a +4 armor bonus to AC.
Unlike mundane armor, mage armor entails no armor check penalty, arcane spell failure chance, or speed reduction. Since mage armor is made of pure force, incorporeal creatures can’t bypass it the way they do normal armor.
The armor holds until the subject has sustained cumulative physical damage totaling 8 points + 1 point per caster level, at which point the spell ends. (The armor does not absorb this damage. It merely grants the armor bonus; the subject still suffers full damage from any successful attacks.)
Focus: A piece of finely cured leather that has been blessed by a priest.