Edge Softness

Edge Softness controls the softness of the edges of the silhouettes of objects with a volume material. For example, a sphere with a low Edge Softness value will have a "hard" silhouette, meaning that you'll be able to clearly see the edges of the sphere. A high Edge Softness value will almost totally obscure the edges of the sphere. This example shows Edge Softness of 0% (left) and 100% (right).