Abstract: The subject invention is a damper apparatus which includes an expandable, rigid frame mounted on an elongated rod. A sheet material flexible cover covers the frame. With the frame located in a collapsed configuration, the frame and cover are inserted through a hole in a duct, and, once inside the duct, the frame is expanded with the cover tightly encasing the frame. With the frame expanded, the cross-sectional area of the duct can be substantially completely closed. The covered frame can be pivoted to any desired position and caused to remain in that position which will function to restrict the flow of fluid through the duct.