On occasion, when Ben Grimm regained his human form and lost his Thing powers, he used a suit of powered battle armor designed by Reed Richards that simulated the strength and durability of his mutated body, albeit to a weaker degree.
It has been revealed - after Franklin and Valeria created a formula that allows Ben to become human for one week each year - that Ben is almost immortal when in his Thing form, as he only ages when he is human.