Treeskin

You touch a willing creature. Until the spell ends, the target's skin has a rough, bark-like appearance, and the target gains a natural armour of 15 + their dexterity or constitution modifier (up to a maximumn of 2). The bark counts as medium armor the target is proficient in (and thus is affected with features such as medium armor master).

At higher levels. When you cast this spell using a slot of 3rd level or higher, the number of targets increases by 1 hour per level of the spell above 2nd.