A flexible duct connects the main ductwork to a plenum box or directly to a circular diffuser. The use of it makes a ventilation system more easy. The flexible hose can be from pvc, textile, aluminium laminate, alumiumn or stainless steel, always reinforced by a wire inside. There are standard , thermal insulated and acoustic insulated flexible ducts with different fire rated executions. The flexible hoses are installed with metal clamps, nylon clamps or tapes to make the ductwork airtight. The air flexible is packed in boxes, for example a 10 meter lenght into a box of only 1 meter .