PHB
Barkskin
2-level Transmutation
Casting Time: 1 action
Range/Area: Touch
Components: V, S, M
Materials: a handful of oak bark
Duration: Concentration, 1 hour
You touch a willing creature. Until the spell ends, the target's skin has a rough, bark-like appearance, and the target's AC can't be less than 16, regardless of what kind of armor it is wearing.