Mulberry silk tops are all natural silk fibers. They are obtained from the cocoons of silkworms feeding on mulberry leaves. I love to use them, so you can find them in many of my products. As they are just another kind of fibers, one can add them to merino wool at the beginning of wet felting process. After felting, they remain on the surface in the form of branched fiber lightnings shimmering with reflected sunbeams.