Designed for low leakage HVAC systems or systems requiring modulating airflow. Typically installed inside ductwork of low to medium airflow velocity and static pressure capabilities. Structurally reinforced frame is constructed of aluminum. Extruded blades are constructed of aluminum utilizing silicone seals. Symmetrical opposed blade configuration allows it to modulate airflow in either direction. Linkage is concealed along frame outside of the airstream. Max air temperature 180ºF.