The fairly long pelage is composed of glistening guard hairs and short, soft underfur. The general coloration of the upper parts is brown to blackish brown, whereas the underparts are whitish or tinged with buff. The feet are not modified for aquatic life to the pronounced degree found in Ondatra, but they do have small swimming fringes. The scaly, scantily haired tail is round. The ears are small and nearly concealed in the fur.
Females have six mammae.
It seems to choose bogs rather than the aquatic habitat preferred by Ondatra. It apparently likes thickly vegetated areas. Although more terrestrial then Ondatra, Neofiber is a good swimmer. It is active throughout the year and is primarily nocturnal. The house rests on a base of decaying vegetation and is composed of tightly woven grass or emergent aquatic plants.