NPH is what Pro 400H used to be called, and NPZ is what Pro 800Z used to be called. I don't know whether or not the emulsions actually changed when the names changed, but I am assuming that at least a minor change was made. I still mention NPH and NPZ because it is still available expired en masse, and still works great if it has been taken care of. I have at least a dozen pro packs of NPH 220 stockpiled, so I won't be using any Pro 400H until that stash is gone. I think I have shot all my stockpiled NPZ, so I am using Pro 800Z now.