Blend blend blend
They revamped this blending brush and made it into a fine white bristle (although some stores may still have the black version), when I asked what it was made out of one of the store reps said "horse". The site says the hairs are natural, but I'm still questioning the reps answers. The brush is VERY rough, you will definitely be able to blend up, sideways & together eye shadows.
Keep in mind, it is a little rough, and I'm sure a lot of people will not be able to stand it's roughness. Sweeping will definitely work, but this brush calls for circular techniques to get the best results with it's blending properties.