Curlex erosion control blankets are biodegradable and designed to promote ideal growing conditions for grass seed while protecting topsoil from wind and water erosion. The blankets have a built-in swell factor; wet curled excelsior fibers slightly expand in thickness and interlock to form a strong fiber matrix. This allows the fibers to provide close contact with local terrain. Water flow is trained to follow the curled fiber matrix. The roughness of the curled excelsior matrix slows the velocity to a point where gravity takes over, allowing moisture to slowly seep into the topsoil.