A prism is a transparent block of glass or acrylic which is shaped like a triangle on each end. Prisms are ideal for experiments on spectrum. These equilateral Prisms are made of true optical glass. Each side is 27 mm, and the length is 75 mm. Ages: 7+. This box is great as a “class pack” or on a store shelf. It includes 20 prisms and a pad of 25 tear off informational sheets.