The attached picture is of flex duct piping for a central heating and cooling system installed 25 years ago. As you can see the insulation that is to insure the heated or cooled air arrives efficiently to the room or rooms it is to heat or cool has lost it's ability...
Flexible Duct Piping has been commonly used for over 30 years in residential and commercial HVAC applications and in ductwork setups. However, just like most man made things - they wear out and break down and are no longer doing what they were originally designed to...