Eucalyptus filiformis is a mallee that typically grows to a height of . It has rough, fibrous to flaky, light grey bark on the trunk, smooth bark above. The leaves on young plants are more or less
sessile, narrow linear, bluish, a slightly lighter shade on one side, up to long and wide. Adult leaves are
petiolate, narrow lance-shaped to narrow elliptical, long and wide. The flower buds are arranged in leaf
axils in groups of seven, sometimes up to eleven, on a
peduncle up to long. Mature buds are oval to spindle-shaped, up to long and wide with a conical
operculum. Flowering occurs in late autumn and the flowers are white. The fruit is a woody, cylindrical to barrel-shaped
capsule up to long and wide with the valves below rim level. ==Taxonomy and naming==