Baetis Mutation Film is a very unique tying material. It is a film that is cut into strips and has a thin paper backing. It is highly reflective but the color of the reflection changes based on the viewing angle. This color change catches the human eye as well as the trout's. My friend Pablo from the Spanish fly fishing team showed me this material when I visited him in Spain. It is great for perdigons or for the abdomen or flashback on other nymph styles.