An expandable media filter structure is composed largely of biodegradable materials and is environmentally disposable. A plurality of pleated panels are interconnected at their edges so as to be collapsible for storage and shipping purposes but expandable for installation and use. A plurality of ribbons are ultrasonically welded to each of the panel edges, wit the ribbon portions between edges being of substantially equal lengths, thereby maintaining equal spacing between the panel edges when the filter is in the expanded condition but allowing an easy collapsing of the filter for storage. Forming a part of the disposable filter are pair of end plates, with each being adhesively attached to an end panel and having a pair of slots formed near their ends for attachment to a nondisposable support structure. The end panels are formed of multiple layers of paperboard which are adhesively bonded and compressed into a U-shaped structure that rigidly supports the filter in its expanded condition. The nondisposable support structure includes a pair of molded plastic side caps that fit over the respective ends of the filter panels and the end plates. Each side cap has a pair of flanges at its opposite ends which act to maintain the filter in its expanded condition when the end plates are placed in abutting position therewith. Each side cap also includes a boss which fits into a respective end plate slot to hold the end plates in their installed positions within the side caps.