GreenGuard is the nation’s leading brand of siding underlayments. Made of extruded polystyrene (XPS), our underlayments provide superior moisture resistance and are perforated to allow moisture vapor to escape. They do not absorb water, are not a food source for mold, and are not subject to moisture-related damage and deterioration. They also retain their insulating properties over time. All of our underlayments are designed to lay flat, giving siding a smooth, even finish. Plus they are lightweight and durable, so they cut easily without crumbling.