An umbrella is one of the most simple and straightforward flash modifiers and, as such, it is one of the most versatile. Reflective umbrellas are designed to have the flash fire into them, reflect, and then bounce the light onto the subject. The umbrella expands the size of the light source, and the resulting light has a broader, softer quality compared to a bare flash. Reflective umbrellas have an opaque covering on the outside to prevent light from passing through and escaping. This ability to contain the light makes it a more efficient light source than a plain white, translucent umbrella through which light passes.
A plain white umbrella with a black backing will offer the most neutral color of light, but compared to the metallic-lined umbrellas, tends to diffuse a bit more and reflect a bit less.