Choosing between Polypropylene and Polyurethane constructions depends on your specific application requirements. If you need a ducting option that is lightweight and flexible, then Polyurethane would be an ideal choice. On the other hand, if you require a ducting option that is more durable and resistant to abrasion, then Polypropylene would be the better option. Both options are designed to meet the most rigorous requirements in terms of heat resistance, weight, durability, and flexibility.