Gosky Optics 4 Color Planetary Filter Set - No.21 Red/No.12 Yellow/No.80A Blue/No.56 Green They are an essential tool of the lunar and planetary observer, for filters permit the observation and photography of surface detail that is often virtually invisible without filtration. Highlight features on Mars, Jupiter, and Saturn. The filter is made of metal and good-quality glass. Not plastic. And it has Anodizing Aluminium process. Metal frame and made of optical glass. Comes in a sturdy plastic case - proect the eyepiece from dust and moisture