Fouling is a leakage current path across the surface of the insulator to the plug body, bypassing the gap. Spark occurs at the point of least resistance, a very small area of the electrode, usually on a sharp edge. A high grade plug with a platinum fine wire electrode would be more resistant to fouling for two reasons: Less area around the center electrode wire to form a parallel path, and a less resistance in the electrode wire itself. In practice this is probably not that big a difference. If the bike fouls one type it will likely foul the other. You can't fix that problem with a plug. I'm running the same basic cheapo BR8ES all year and its fine.