Physical damage shields?

I've been wondering for a while now, why is it we have magic damage shields and shields that can block all damage, but there is no physical damage shields? Would it be a good addition to the game? Thoughts?

Edit: The idea is that the AD shield would be able to shield more damage than a normal shield since AP damage can still get through. Something like that had to get nerfed right after it's release cause it's shield was too effective, could have a physical shield that instead, which allows it to shield more, but still has an exploitable weakness through AP damage.