The Westcott 4633 Silver Diffusion Parabolic Umbrella (213cm) is an umbrella with an arc length of 213cm that is suitable for use with any studio flash set.
With an umbrella you generate a slightly harder light than with a softbox, but the light is softer than when you point the flash directly at the subject.
A pop-up umbrella is particularly ideal to prevent hard shadow lines and in situations where there are several light sources and you use one or more umbrellas as fill-in flash.