replying to gofish, Divine Design wrote: Flex duct is garbage, it causes drag on air flow. Critters love making nests in it!!!! Properly installed and insulated tin can be done easily during construction phase. As long as good communication between contractor, homeowners and company doing system is in place. I have had houses with nothing but hard insulated duct, houses with flex duct and a house with a combination of both. We have had repeated problems with flex and only one problem with the hard duct. The ceiling registers sweated, (we live in FL where humidity is extreme) this was easily remedied by installing thermostatically controlled attic vent fans. We installed two, our house was 3000 sq ft. We put one on each side of our attic. We also added extra installation to our vent. Never had another problem. All of this can be done as stated during installation. When we built our last house all duct was run of course prior to drywall installation so techs had full access to duct with no obstruction to doing their work. It?s what they do every day and know all the tricks to making sure all joints, screws etc are sealed with duct sealant, then ducts are wrapped in insulation (choose the highest R rating you can possibly afford) and then installation joints are taped. Following thsese steps will give you a system that will far outlast your lifetime. Flex duct will give you nothing but restricted air flow, critters, lost $$$$ a lot of headaches.