My 1976 flex duct in the attic is showing signs of age - it's brittle and in some places caved in. I've read some of the threads on this site with regard to the economy of replacement and from what others have said I have come to realize replacement may require a lengthly payback period.

We plan to stay in our house for twenty or more years. If we change the flex it should be now, not later. I am considering a long metal duct with flex running off of it but that will more than likely involve too much attic floor space to be useful and still leave enough room in the attic to walk around in.

Going back to the question of replacing the flex, I am wondering if there have been any advances in this product. With energy conservation so very important has anyone produced a "super flex" - even at a much higher price or do the laws of physics apply and limit the benefits beyond the current price/performance design of the product?