Hubble Space Telescope narrowband images of four PNe resolve the microstructures in four PNe known to contain FLIERs (e.g. Balick et al 1994). FLIERs are seen to fall into two morphological groups: very low ionization clumps of small knots with cometary-like tails, and sinewy transverse filaments with fainter extensions pointing outward from the nucleus. Generally speaking, FLIERs exhibit [NII]λ6584/Hα > 1. They are marginally detectable in Hα above the bright background of nebular emission, and all but invisible in [O III]λ5007A. In every case the star-facing side of the structure is on the order of a pixel in width (about 1015 cm). A decreasing ionization gradient is seen [O I]λ6300A, [S II]λ6717 + 31A, and [N II]λ6584A images.