It’s generally better to apply window film on the inside of windows rather than the outside.

Here’s why an inside application is usually recommended…

Protection from the Elements

• Durability – The interior application protects the film from weather elements such as rain, snow, and direct sunlight, which can degrade the film more quickly when applied outside.
• Longevity – Films applied inside are shielded from environmental wear and tear, extending their functional lifespan compared to those applied externally.

Ease of Maintenance

• Accessibility – It’s easier to clean and maintain window film when it’s applied inside. External films can be more challenging to access, especially on upper floors.
• Protection – Inside-applied films are less likely to be damaged by cleaning or maintenance activities that could affect films applied to the exterior.

Efficiency and Effectiveness

• Performance – Many window films are designed to function optimally when applied to the interior of the window, particularly those intended for energy efficiency, UV protection, and glare reduction.
• Installation Conditions – Applying film indoors allows for better control over the installation environment, such as avoiding dust, wind, and fluctuating temperatures that can affect the application process.

Safety and Security

• Security Films – Films designed to enhance window strength and prevent shattering (such as in the case of break-ins or accidents) are more effective when applied to the interior side of the glass.
• Privacy – Privacy films work based on light differential. Applying them inside helps maintain the intended effect without being compromised by external conditions.

Considerations for External Application

While the internal application is generally preferred, there are situations where an external application might be considered necessary…

• Window Type – Some types of windows or glass coatings may not be compatible with internal films. For example, windows that are already treated or coated, or certain types of double-pane windows, might require external films to avoid thermal stress and potential damage.
• Specialized External Films – There are films specifically designed for external use, formulated to withstand weather conditions and UV exposure better than standard films. These might be used in cases where internal application is not possible or practical.

Conclusion

Applying window film on the inside of windows is usually the best option due to the benefits of protection from the elements, ease of maintenance, optimal functionality, and overall longevity of the film. Regardless, every situation is unique, and factors such as the specific type of window, the purpose of the film, and the manufacturer’s recommendations should be considered when deciding the best application method. Consulting with a window film professional can provide guidance tailored to your specific needs and circumstances.