It is said that glass flake was developed in the United States around 1959 and was used initially for the reinforcement of what was, at that time, new-technology roof-light panels made from a polyester resin. However, it was found that the panels distorted in strong sunlight and a means of improving modulus and dimensional stability was sought. Glass fibre, although it provided improvement when used at the required volume for stiffness, severely reduced light transmission. Apparently, when glass flake was used not only was the modulus substantially improved but also light transmission. Although this seems to have been one of the first commercial uses of the product, glass flake quickly found its way into the coatings industry and it is here that the bulk of flake was used for many years and where most investigative work was carried out, only later progressing into other materials. As much of the research and development work with glass flake, and hence understanding, has been carried out with coatings, it is through these materials that we can introduce most of the facets of incorporating glass flakes into product.