An adjustable filler panel assembly, configured for use in an electronic equipment enclosure, includes a first panel and a second panel, each adapted to block airflow. The first panel has pairs of horizontally aligned adjustment openings formed therein, and the second panel has a pair of horizontally aligned attachment members disposed near one end. The first and second panels are connected to one another in an overlapping arrangement to form an air-blocking panel assembly with the attachment members of the second panel being aligned with and connected to a pair of adjustment openings of the first panel. In addition, the first panel and the second panel are telescopically adjustable relative to one another such that a length of the air-blocking panel assembly is selectively adjustable to fill at least a portion of an opening in the electronic equipment enclosure, thereby blocking air from flowing through the opening.