Darker glass (blackout film) can absorb a lot of heat, and this can lead to huge stress on the glass. The result could be glass breakage due to thermal stress.
Glass breakage can also occur when the glass panes are not properly installed. In most cases the edges of the glass would either be damaged or chipped before the window film was applied. This can cause the cracking glass after application.
If glass is tempered, the installation of black out window film is unlikely to result in the glass fracturing or cracking.
There are other window film options that provide privacy, such as patterned, white frost and other decorative films.
If you are looking for privacy through window films, ask your window tinting professional which films would be recommended on your windows. There usually is a product available to meet your needs! Check out some of our decorative film options.