Before picture shows a typical attic heating, cooling and duct system. The main metal trunks and plenums are not sealed and only have a 1/2" liner inside. The results are in the summer when the system is trying to deliver approx 57 degree air through ducts, that are heating up to 130 degree surface temperatures, they lose a tremendous amount of energy. In this case the system was not keeping up with demand on hotter days. The opposite is true in winter- ducts try to deliver 110 degree air through ducts that are cooling down to 30 degrees or less. The after picture shows Duct Encapsulation, the duct system is sealed and insulated with approx 3" of closed cell spray foam. This impoved the peformance of the duct system by 40% or more and now the system keeps up even on the hottest days!! If you have a modern system it makes sense to upgrade ducts, instead of installing a larger more expensive system to solve the problem.