The Add Dust filter adds curled, grey, dust-like elements to the active layer.
Density controls the amount of dust elements that will populate the layer. A setting that is too high here can become extremely processor-intensive, so adjust this setting carefully.
Seed is the numeric randomization base. Changing this number will result in different dust element shapes and positions.
Length controls the length of the dust artifacts. A higher setting here will result in longer curls of dust.