Holographic films with an iridescent finish let part of the light that strikes them through and reflect part of the light source with different refraction indexes. The interaction between different light rays reinforces certain wavelengths while eliminating others, so that the colour with the most intense matrix increases by a number of wavelengths and appears more intense depending on the angle of reflection. If the angle of observation is changed perpendicularly, the wavelength of the reflected light drops in intensity, thereby modifying the hue perceived. Holographic sheets, appropriately cut and mixed with fibres, are used to laminate plastic films for making bags, shoes, clothes, etc.