The choice of window film depends on the level of darkness you desire. For single pane glass, any film will work effectively. However, when it comes to double glazed units, the selection process becomes slightly more intricate. If the pane you intend to apply the film to is toughened, then any grade of film can be used. However, if the pane is not toughened, you will need to opt for a lighter film option or consider using an external grade film. To ensure the compatibility of the film with your specific requirements, please review the product's specifications and compatibility data before making a decision.