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 , with 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 planes 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 .