Sanjeev Sabhlok's notes on technology, hardware, gardening

Reducing heat from windows in summer: paint, film, blinds, hoods, awnings

Go to and search for ratings of various films.

A Window Film Review

Unshaded glass is the single greatest source of unwanted heat in a home. When sun passes through glass it is absorbed by building elements and furnishings, which then re-radiate it at a different wavelength. This new wavelength cannot pass back out through glass and is ‘trapped’ within the house. This is often referred to as the greenhouse effect which results in higher temperatures indoors compared to outdoors. [Source]

Exterior awnings are by far the best option in reducing direct sunlight. For internals Plantation shutters > Double roller blinds > Cellular blinds > Venetians [Source]

Low-e glass

heat transfer through windows in either direction is via both conduction and radiation. Low ‘e’ glass and films reduce the radiant heat transfer and keep the heat in addition to keeping the heat out. [Source]


A window covering is a shade or screen that provides multiple functions. For example, some window coverings control solar heat gain and glare. There are external shading devices and internal shading devices.[24] Low-e window film is a low-cost alternative to window replacement to transform existing poorly-insulating windows into energy-efficient windows. For high-rise buildings, smart glass can provide an alternative. [Source]

Window covering

Velcro DIY fitting

See details here.

Window film

window films are good at stopping radiant heat (ie. direct sunlight, or heat radiated off hot surfaces such as adjacent paving or a masonry wall) they’re not so good at stopping convective heat, which is where double glazing has its advantage. [Source]

Films work well in rejecting radiated heat, ie sunlight shining thru the window. [Source]

I had some film applied to my eastern & western windows by a professional firm a few year ago- from memory they advertised about a 65% heat reduction. My unscientific feeling is that the heat reduction was significant and around 65% seems reasonable. [Source]

We had the window tinting on the front windows of our home replaced last year as a lot of the previous 15-20 year old film was turning purple and starting to peel off. We went for a much darker film this time as the windows are exposed to the full summer sun here in Perth. The rooms definitely take longer to heat up which is great in summer but not so good in winter. [Source]

I assume you refer to the metallic solar films which have been around for a donkeys years and are designed to exclude incoming heat through glass windows. In which case, yes they do work. The east facing sun-room before having solar film applied was a sweat box. After application of lightly tinted (metal based?) film, it only averages about 2 degrees C above the rest of the house. [Source]

I can vouch for the effectiveness in Summer of the application of retro fitting tinted film to our home office West facing sliding glass door and overhead diffuser acrylic panels below a West facing roof skylight. Without these the temperature in Summer was unbearably hot and the air conditioning had to be turned right up even though the the door faces onto a 2 metre wide patio and ceiling and walls were fully insulated. Since application several years back now the office is very much cooler and air conditioner only needs to be occasionally turned on and then not fully ,so this was a very economic measure regarding power consumption also. The reverse side to this is that with tinted glass or tinted film during the day you can see clearly out whilst those outside cannot see inside. [Source]

I’ve had films installed on all our windows facing west (which was our problem area), which has reduced the heat coming in dramatically, and the cost was only about $400. It’s a no-brainer for me! [Source]

Our house has a lot of ENE facing windows and a large NW facing window in our bedroom. We got them tinted and it made a massive difference to the heat that comes in compared to without the tint. Tinting is also fairly cost effective, we had 11 fairly large window areas (Most of the windows had at least 1 if not 2 awning wind out openings) which all up cost us just over $2k to have done. As an added bonus we didn’t have to put up any sheer as during the day you can’t seen in the windows. [Source]

3M film

It was expensive but we applied 3M sun control window films to the areas were the afternoon sun hits. The difference in temperature was remarkable. These are multilayer optical films which reject over 90% of the suns infrared light. It is very likely that they will work both ways and also reflect heat back into the room.

These foils look like a mirror from the outside preventing people looking through the window even at close up. From the inside it looks like a tinted glass. Again, the issue with us was to keep the sun radiation out which worked well.   [Source]

We have a 3M brand metalic film on 4 east facing windows. It does cut down heat, you can definately feel the difference when you slide the window open and alternately stand behind the shielded and unshielded portions. Not sure how much heat is reduced overall in the room though. In the daytime yo cannot see in from the outside which may or may not be beneficial depending on if you want to be able to see in from the backyard etc, and at night time you cannot see out of the windows because of the reflection. The aluminium frames still get as hot as normal and radiate as much heat into the room as normal. On a hot day, the glass still gets hot no matter what, which does radiate heat into the room. The only real way to protect a window is to shade it completely with either trees, awnings or roller shutters. We have roller shutters on our North and West facing windows and they do a much better job. A lot more expensive though. [Source]

This website has a good discussion of window films (

I don’t like losing out the views on “good” days, so the film must not block views.

Smart film


An old trick is to build a trellis outside the north windows and grow vines or other seasonal plants on it – provides shading during summer but is mostly bare during winter. [Source]

we have a pergola with deciduous climbers over the north windows and an external blind over the west. They both work extremely well, blocking the sun in summer whilst still permitting sunlight for solar heating in winter. (The climbers we have are Wisteria which provides a colourful flower display in spring and Virginia creeper which provides a colourful autumn leaf display.) [Source]


There is a large difference in performance with the different blind types and materials as there is with the different films types. So it is possible to install internal blinds that have similar reflective properties to some tinted films. However:

  • as there are films that have almost no reflective properties it is an easy claim to make that their reflective blinds have similar reflective performance to tinted films, (i.e. the blind manufacturers claim is not comparing apples with apples).
  • reflective films have a greater impact on the appearance of the windows. I.e.They add a tint (typically grey) and therefore change the colour of your view and they are very reflective from outside during the daytime often to the extent that the appear as mirrors impacting on the aesthetics of the building or creating unwanted glare etc. (With the reverse mirror effect at night.)
  • the films will also reduce the solar heat gain during winter which you may want to reduce heating bills.

I was thinking of some kind of guide to close the gap between the blind and window frame (on the side). Anyone seen these anywhere? Verosol have them: Verosol used to be the industry benchmark but were not cheap. I don’t know if they still are.

You could also consider this film: They claim that they have films that have a low E coating and can provide equivalent heat gain/loss performance to clear double glazing. Films with varying SHGF and reflectivity are also available. (I have not used them nor know of anyone who has and only came across this product from another thread.) [Source]

Bubble wrap

I havent used those applied solar films but have used bubble wrap!!! it did work! [Source]

Friend of mine was looking into this found a new lot that was self install, cut out the other guy, she has decided to use bubble wrap instead, seems to be working [Source]

Aluminium foil


Window blind

Shading devices

blinds of any kind inside the room will do nothing for reducing the heat from direct sunlight. Highly reflective metal blinds might do a bit better than timber, but both will simply heat up and all that heat will be radiated and convected into the room. [Source]

Note that neither will double glazing do anything for direct sunlight. Double glazing is an idea popularised by their use in Europe where the main issue is keeping in heat, and they are highly effective at doing that. Similarly, if the window is shaded, double glazing will reduce flow of convective heat from the hot outside air, but if the sun is shining through it, the radiant heat will go straight through it. [Source]

Window tinting with an appropriate metallised foil would be somewhat effective at reducing the heat from direct sunlight [Source]


Venetians do help but the heat has penetrated the window already. [Source]

I tried various things and the most effective and cheapest is painting the outside of the glass with white acrylic paint. If you change your mind it is easy to scrape off with a paint scraper. [Source] ” for this to work effectively the paint needs to be on the outside.

Cellular blinds

Sail-shade cloth

Can’t be installed higher than 4 metres high. Beyond that the requirements for support become extremely high due to wind etc. pressure.



Reduce the size of the window

window films are good at stopping radiant heat (ie. direct sunlight, or heat radiated off hot surfaces such as adjacent paving or a masonry wall) they’re not so good at stopping convective heat, which is where double glazing has its advantage. [Source]


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