Abstract: A tunable blob function is proposed which is computationally simple since it is a rational function of low degree. The blob function is dependent on a parameter d which can be used to control the blob function making it suitable for computer graphics applications such as implicit surface generationl. The main properties of the blob function are described and graphed. When the parameter d is large, the blob function can be used to generate a three-dimentional spike by rotating it around the z-axis.