The Cokin Filter P091 Dreams 1 is processed in such a way that it creates halos around highlights. This effect becomes extra-obvious when light subjects are set against a dark background. For example, white flowers against a dark curtain or streetlights against the evening sky. The great advantage of this type of diffusion is that even though the effect creates an overflow of highlights, the image remains sharp.
It is advisable not to use an overly large aperture, otherwise you get double contours instead of dreamy halos. When using this technique, it is also advisable to use bracketing, especially if the subject is exposed from behind.