Smooth-sheathed sedge is a graminoid with 4-20+ spikes per inflorescence. lateral spikes that are staminate or pistillate, sessile, and prophyllate, terminal spike is staminate. Its culms are 40cm-1m. Perigynia are pale brown, red-brown distally, with red-brown veins, cordate, achenes are ovate, persistent style base is cylindric. Sheaths all have blades, fronts are smooth, lacking spots, veinless, apex is yellow, thickened, truncate, cartilaginous, entire. Ligules are acute, 5mm, free limb to 0.5mm, blades are yellow-green, epistomic (with stomata confined to the adaxial or upper surfaces), papillose adaxially. Its scales are hyaline.
It is readily distinguished from all other species in the Vulpinae section by its thickened, yellow sheath apex, smooth sheaths, and the papillose, epistomic leaves (with stomata only on the upper leaf surface). It's most similar to Carex stipata, which has leaf sheaths that are puckered or wrinkled and thin or broken (not thickened) at the apex.