Air ducts are typically made from metal, fiberglass, or plastic materials depending on the needs of the HVAC system. Metal is generally considered the most durable type of material while fiberglass may be a better option if you’re looking for more insulation properties; however plastic is often used in areas where space is tight since it’s lightweight yet still provides adequate insulation against cold temperatures and moisture buildup. Additionally, some types of air duct systems may be insulated with additional materials such as foam-based products in order to help maintain the desired temperature without losing energy efficiency.