This incredibly rare and hard metal represents the pinnacle of non-magical wall strength. Treat weapons and armour crafted from obdurium as adamantine, except for hardness (30), hit points (60 per inch of thickness, or twice as many hit points as a typical item) and price (twice the listed price for adamantine).
HP: 60 per inch of thickness; Break DC: 48 + 4 per inch of thickness.
Source: Stronghold Builder’s Guidebook (Page 35)