Which characteristic of ducts is essential for preventing air leakage?

Airtightness is crucial in preventing air leakage within ducts. This characteristic ensures that air is properly contained within the ductwork without leaking into surrounding areas. When ducts are airtight, they maintain the efficiency of the HVAC system by ensuring that the conditioned air reaches its destination without losses. This not only optimizes energy consumption but also contributes to better comfort levels in a building by avoiding drafts and unconditioned air infiltrating living spaces.

In contrast, while durability can enhance the lifespan of duct systems and flexibility may allow for better installation in various building designs, these attributes do not directly influence air leakage. Weight is also not a determining factor for preventing air leaks; it is more relevant to the ease of installation and structural support requirements. Thus, airtightness stands out as the key characteristic necessary to effectively control air leakage in duct systems.