Russet cotton-grass is a graminoid with single spikelets that are erect at end of stems and clustered in a roughly round head 2-3 cm wide. Flower scales are narrowly ovate, black-green, with broad white margins and tips, bristles are white to bright red-brown. Its dark brown achenes are oblong-obovate, 2-2.7mm, one third as wide, and distinctly apiculate. It has few leaves, mostly near the base, narrow, channeled, or triangular blades, 1-2mm wide. The uppermost leaves are from near middle of stem and often without blades.