How mucus moves: the lining of the sinus is covered with tiny hair-like structures (called cilia) that constantly sweep fluid toward the sinus drain. The mucus the lining makes always travels along the same path, set by the direction those tiny hairs beat. In a healthy sinus, a thin blanket of mucus is always slowly moving along. The top layer is thicker and gel-like, while the layer underneath is thinner and more watery.