Kind of dumb they nerfed the negative to metal for druids, 3.5 used to be:
A druid who wears prohibited armor or carries a prohibited shield is unable to cast druid spells or use any of her supernatural or spell-like class abilities while doing so and for 24 hours thereafter. This was about the same for multiple other classes also (having negative effects that is).
There was this also:
A druid may also wear wooden armor that has been altered by the ironwood spell so that it functions as though it were steel. See the ironwood spell description, page 246)
dnd.arkalseif.info
