Instax is based on the old Kodak Instant Film. It uses a reversal emulsion and dye releasing incorporated developers. It is exposed from the emulsion side through a clear cover sheet that has a timing layer the breaks down allowing an acid compound on the cover sheet to stop the development process. Notice that since it exposed through a cover sheet, the cover sheet can containing a color filter allowing for color correction to the media. The color dyes that are released in development diffuse into a TiO2 layer that produces the image.