Low-E Window Film: Does It Keep Heat In During Winter?
Yes, Low-E window film does keep heat in during winter. It works by reflecting the warmth from your heaters, your furniture and even your body back into the room instead of letting it escape through the glass. On single glazed windows, official Solar Gard figures show Low-E film cuts heat loss through the glass by around 40%.
Most people think of window film as a summer product. Low-E film is the exception: it’s designed to work all year round. This guide explains how it works, what the real numbers are, and whether it’s worth it for your home.
Why windows lose so much heat in winter
Glass is a poor insulator. On a cold night, a single pane of glass is the weakest part of your wall. Warmth inside your home escapes through the glass in two main ways:
- Conduction: heat moving through the glass because the inside is warmer than the outside.
- Radiation: warm objects in the room give off long-wave infrared heat, which passes into and through the glass.
That’s why you can feel cold air “falling” off a window on a winter evening, and why rooms with big windows are always the hardest to heat.
Insulation performance is measured by the U-value. The lower the U-value, the less heat escapes.
How Low-E window film works
“Low-E” stands for low emissivity. A Low-E film has a microscopically thin coating that reflects long-wave infrared heat.
In winter, that coating faces into the room. When warmth from your heater or furniture radiates towards the window, the film reflects much of it back inside instead of letting the glass absorb it and lose it to the cold outside.
In summer, the same film also rejects a share of the sun’s heat coming in.
The real numbers: Solar Gard Ecolux
Here are winter U-values from Solar Gard’s published figures. Lower is better.
| Glass | Winter U-value (W/m²°C) |
|---|---|
| Single 6mm clear glass | about 5.6 |
| Single 6mm clear glass with Ecolux 70 | 3.42 |
| Standard double glazing | about 2.7 |
| Double glazing with Ecolux 70 | 1.93 |
What this means in plain terms:
- Adding Ecolux to single glass cuts heat loss through the glass by about 40%.
- Single glass with Ecolux gets surprisingly close to standard double glazing.
- Double glazing with Ecolux is the best result of all.
And in summer, Ecolux 70 on 6mm clear glass:
| Measure | Ecolux 70 |
|---|---|
| Visible light let in | 67% |
| Total solar energy rejected | 53% |
| UV blocked | more than 99% |
| Glare reduction | 25% |
So you get a near-clear film that helps in both seasons. For a full comparison with double glazing, read window film vs double glazing.
Which rooms benefit most?
Low-E film makes the biggest difference where:
- Windows are large, such as living rooms with sliding doors or floor-to-ceiling glass
- Glass is single glazed, which is still common in older Sydney homes and many apartments
- Rooms are hard to heat, like open-plan areas with high ceilings
- Windows face south, getting little winter sun but losing heat all day
- You run heating for long hours, such as in a home office or a baby’s room
In western Sydney, the Blue Mountains foothills around Penrith, and Picton and Wollondilly, where winter nights get properly cold, the difference is very noticeable.
Will Low-E film lower my energy bills?
It can help, but be wary of anyone promising an exact figure. Savings depend on how much glass you have, how well the rest of your home is insulated, how long you heat and cool, and your energy prices. What the U-values show is that less heat escapes through the glass, so your heater works less to keep the room warm.
For an estimate based on your windows, try our energy savings calculator.
Low-E film vs other ways to keep heat in
Heavy curtains
Good at night when closed, but they block your light and view during the day, and gaps at the top and sides still let heat escape.
Double glazing
The best insulation, but it means replacing windows or sashes, which costs far more and takes longer. See can you tint double glazed windows if you already have it.
Secondary glazing
A second pane fitted inside the existing window. Effective, but bulky and visible.
Low-E window film
Fitted to your existing glass in a few hours, close to invisible, and works day and night, winter and summer.
Is Low-E film the same as normal tint?
No. Normal tinting films are designed mainly to reject solar heat coming in. They do little for heat escaping on a winter night. Low-E films are specifically designed with the low-emissivity coating facing the room, which is what gives the winter benefit.
If your main problem is summer heat, a standard heat reduction film may be enough. If your problem is cold rooms in winter, or both, Low-E is the better choice. Read does window tint really reduce heat in a house? for the summer side of the story.
Things to check before installing
- Glass type: most clear float glass suits Low-E film. Some tinted, laminated or double glazed units need checking first, because film raises glass temperature.
- Condensation: Low-E film keeps the room-side surface of the glass warmer, which may help with condensation, but it won’t fix a home with very high humidity or poor ventilation.
- Cleaning: wait a few weeks after installation before cleaning, then use a soft cloth and mild soapy water. Avoid abrasive pads.
How long does Low-E film last?
Professionally installed Solar Gard films come with manufacturer warranties from 10 years to lifetime, depending on the film and whether it’s a home or a business. Low-E films have a coating that faces into the room, so they need gentle cleaning: a soft cloth and mild soapy water, with no abrasive pads, blades or ammonia-based cleaners.
The bottom line
Low-E window film does keep heat in during winter. On single glazed windows, Ecolux 70 cuts heat loss through the glass by about 40%, getting close to standard double glazing for a fraction of the cost and with no window replacement. It also rejects over half of the sun’s heat in summer and blocks more than 99% of UV.
As a Solar Gard Authorised Dealer, we install Ecolux with the manufacturer’s warranty. See our Low-E window film page, or send your window sizes through the free quote form.
