What is the purpose of lining a duct with thick insulation and perforated metal?

Lining a duct with thick insulation and perforated metal serves primarily to reduce the noise generated by air movement within the duct system. The perforated metal helps to attenuate sound waves, while the thick insulation provides a barrier that can absorb and dampen vibrations and noise. This combination helps to minimize the sound that travels through the ducts, making the overall system quieter, which is particularly important in residential and commercial buildings where sound can be a significant concern.

While the other options address important aspects of duct design, they do not reflect the primary purpose of using thick insulation and perforated metal. Preventing condensation relates to moisture control, enhancing airflow focuses on optimizing the movement of air, and improving thermal conduction involves the transmission of heat, neither of which is the main intention of the insulation and perforated lining.