Opalux exterior grade window films have been developed and manufactured to state of the art technology and used successfuly over many decades. They are of weatherable construction having additional UV barriers to help protect the film from degrading through exposure to sunshine, and also having a strong waterproof adhesive.
Opalux exterior reflective solar control films are often fixed to the exterior face of the window glass to reject the heat of the sun before it penetrates and is absorbed by the glazing unit itself. They are therefore more efficient in their primary object of reducing the solar gain by preventing absorbed heat-of-the-sun being re-radiated to the interior of the building, especially where you have extra thick glass or double or triple glazing.
Another reason for fixing to the exterior face of the glass is to reduce the risk of thermal fracture. This particularly applies to laminated, Georgian-wired and heavily tinted glass, and may also apply to double or triple glazing in certain circumstances. Your Opalux Dealer should help you assess the risks and balance the probabilities
Exterior fitting is frequently needed to obscure boarded up windows, spandrel panels etc where access from the inside is not possible or where patterned glass is rough side facing in.
Some Opalux safety & security films are available in exterior grade and are used where there is a risk to people outside the building. An example of this is where spontaneous shattering has proved to be a risk factor from nickel sulphide poisoning having occurred within the particular batch of glass during the manufacturing process.