There's very little difference between an improved Sofa Pillow and a Stimulator. Sofa Pillows are imitative of adult salmonflies, while Stimulators do well imitating smaller stones and caddis.

While the original Sofa Pillow with its unadorned floss body and squirrel wing may be classic in appearance, it won't stay on top as long as the improved version or the Stimi will.