Transmutation
Level: Sorcerer 2, Wizard 2
Components: V, S
Casting Time: 1 standard action
Range: Touch
Target: Suit of armour touched
Duration: 1 round/level (D)
Saving Throw: None
Spell Resistance: No
With a word and the sudden opening of your hand you complete the spell. Touching a suit of armour instantly causes the armour to sprout long, deadly-looking spines.
The bristle spell temporarily enhances one suit of armour, causing it to grow long hard spikes that stick out in all directions. This spell does not work on clothing other than armour, but it does function with armour that already has spikes built in. The spikes are flexible enough not to hamper the creature wearing the armour. Each round, the first time the armour wearer attacks a target in melee, the spikes strike out as well, growing in length and hardness. The spikes have an attack bonus equal to your caster level and deal 2d6 points of damage. Your Strength modifier does not apply to this damage.
Source: Spell Compendium (Page 40)