Product review (5 stars): Exccellent price, fast delivery, stylish, heat and damp resistant (beware its fragility when handling it!)
Exactly what I wanted.  As others have noted, it's very fragile -- it's basically an Alcan foil tube -- so you must be very careful in stretching it out and, in handling it generally.  However, once it's installed in place, it's very durable - heat and damp resistant needs much less support to prevent sagging than other types of (heavier) ducting.  It's way better aesthetically than the 5" white plastic ducting that came with my portable air conditioner.