BF indicates the cells entirely made from borosilicate glass, the composition and properties of which are laid down by an international standard. This type of glass possesses a high chemical resistance and a low thermal expansion coefficient making it particularly suitable for its use as laboratory glassware. For the windows of these cells we use a borosilicate glass manufactured using the float process. An empty cell made from this material has a transmission of greater than 80 % at a spectral range of between 330 nm and 2500 nm.