Corning FluoroBlok Cell Culture Inserts are designed with a unique light-tight PET membrane that efficiently blocks the transmission of light within the range of 400-700 nm. Fluorescently labeled cells present in the top chamber of the insert are made invisible by the Corning FluoroBlok membrane. Once labeled cells migrate through the membrane, they are no longer shielded from the light source and are easily detected with a fluorescence plate reader. Corning FluoroBlok Cell Culture Inserts are designed with a unique light-tight PET membrane that efficiently blocks the transmission of light within the range of 400-700 nm. Fluorescently labeled cells present in the top chamber of the insert are made invisible by the Corning FluoroBlok membrane. Once labeled cells migrate through the membrane, they are no longer shielded from the light source and are easily detected with a fluorescence plate reader.