Platinum and Iridium plugs perform at a lower level than copper spark plugs, because they are less conductive and they tend to overheat. Iridium has its melting point at 2450 degrees, which is more than the platinum. However, the overall longevity of these two types of metal is better than copper plugs. In reality, copper has the best performance of all three and the worst longevity. Platinum has good longevity and the worst performance. Iridium has good longevity and a performance that is decent, which is why iridium plugs tend to be more expensive than any other type. Still, the difference between these plugs in terms of overall quality is minimal, as there is a trade off for each.
A standard material spark plug traditionally uses a nickel-alloy outer material fused to a copper core.