Here's what I THINK I know on OEM vs aftermarket seats...OEM seats incorporate a plastic film under the vinyl which prevents moisture from traveling into the foam. The downside of that is the seat no longer "breathes" and can be uncomfortable in hot weather. Aftermarket seats, OTOH, may use the same or similar premium grade of marine vinyl for the cover but eliminate the underlying plastic vapor barrier. As a result, the seat is more comfortable in hot weather but water can travel through the vinyl into the foam. Often, rain covers are provided with the aftermarket seats. Note: Any seat manufacturers reading this, feel free to correct me if my understanding is in error.