What are the differences between HVAC installation types? In the last few years, most people use flex ducts in their homes. Just as you might expect, flex for HVAC is a flexible duct that has a rough interior and it's insulated on the outside. The only issue is that they can easily compress, and really restrict air flow. It costs more money to switch from a flex duct to a rigid duct, however, some homes utilize both flex ducts and metal ducts. The amount of flex duct is often restricted to a low number per home. Metal ducts are long lasting, better air flow, easy to clean, not effected by UV rays, easier to install," but can be more expensive unfortunately. Watch the full video to learn about the pros and cons of each duct work.