Exterior - vs Interior Solar Window Film.
Choosing between interior and exterior solar window film is essential for performance, safety, and long-term durability. While both options reduce heat, glare, and harmful UV rays, installing the film on the wrong side of the glass can lead to serious problems — including glass damage.
Unfortunately, many installers still make this mistake. That’s why working with Out of the Sun in Spain is so important.
Exterior vs. Interior Solar Window Film — What’s the Difference?
Choosing between interior and exterior solar window film is essential for performance, safety, and long-term durability. While both options reduce heat, glare, and harmful UV rays, installing the film on the wrong side of the glass can lead to serious problems — including glass damage. Reas all the facts for solar window film.
Common Installation Mistake (and Why It Matters)
Many installers incorrectly apply solar window film to the inside of reinforced or laminated glass.
Consequences of wrong installation:
❌ Glass cracking due to thermal stress
❌ Reduced performance of the film
❌ Voided product warranties
❌ Safety risks over time
This is not just a small error — it can lead to costly replacements and structural damage.
How to Check What Type of Glass You Have
1. Look for markings
Check the corner of your glass for labels such as:
- “Tempered”
- “Safety Glass”
- “ESG”
- “Toughened”
If you see any of these, your glass is reinforced and requires exterior film installation.
2. The Simple Sound Test
You can also perform a quick sound test:
- Tap the glass gently with your knuckle or a pen
- A sharp “ping” sound → usually non-reinforced glass (interior film is suitable)
- A dull “thud” sound → laminated or double-glazed glass (often requires exterior film)
Test around your property:
- Sliding or patio doors → almost always reinforced → exterior film
- Skylights or roof windows → reinforced → exterior film
Standard windows → usually suitable for interior film
Interior Solar Window Film.
Interior solar window film is installed on the inside surface of the glass.
It is the most common solution because:
It is protected from weather conditions and it offers excellent heat rejection.
It reduces glare and blocks UV rays and it is ideal for homes, offices, and apartments.
This option works best for:
- Standard single-glazed windows
- Most double-glazed windows
- Typical residential and commercial glass
Exterior Solar Window Film.
Exterior solar window film is applied to the outside surface of the glass. It is required when the glass cannot safely absorb additional heat from the inside.
This includes:
Tempered -, laminated - or reinforced glass
Skylights, sliding doors and roof windows
Sliding doors are often made from reinforced (tempered) glass because they are:
- Large and more exposed to impact
- Frequently used
- Required to meet safety standards
This type of glass is stronger and safer, but it also retains more heat. Applying film on the inside can trap heat between the film and the glass, leading to thermal stress and even cracking.
Why Professional Installation Matters
Choosing the correct film is only half the job — correct placement is critical.
At Out of the Sun in Spain our specialists:
- Identify your exact glass type ( even from a picture )
- Recommend the correct film (interior or exterior)
- Ensure safe installation
- Protect your warranty
- Prevent costly mistakes
We offer free inspections in Spain, so you can be confident your installation is done right the first time. Our solar window film installation services are possible when you live in Malaga, Granada, Almeria, Murcia & Alicante provinces in Spain.
Why Choose Out of the Sun in Spain?
Out of the sun in Spain is widely recognized as one of the most specialized solar window film companies in Spain. With more then 50 years experience in getting people, houses and offices "Out of the Sun" founded in Netherlands in 1973
What sets us apart:
Deep expertise in glass types and thermal behavior.
Precision installation techniques.
High-performance film solutions.
Focus on safety, durability, and results.