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Glass Compatibility: Perfect Fit with Window Film

Make Sure You Select The Right Window Film For Your Glazing

It is imperative that you check and understand the compatibility data for solar films in particular as Purlfrost Ltd cannot be held responsible for problems or damage resulting from applying a film that is not compatible or recommended for your type of glass.

We recommend that you do not apply film in the following conditions:

  • To glass which is visibly or otherwise damaged.
  • Unless using a frosted product, do not apply solar control films to part of the glass to avoid excess load in some areas and not others.
  • Do not apply any film to triple glazed units.
  • Beware that combining solar film with heavy close fitting drapes or curtains can add an extra load to the glass, especially on double glazed units when not made of toughened glass.
  • Do not apply solar control film if the glazing is near a heating or cooling air vent aiming at the glass.
  • Do not apply any film to textured glass, or domed skylights.
  • Do not apply solar films to Georgian wire glass.

If you are not 100% sure that the film is compatible with your glazing, for windows or panes larger than 3m2, or for any advice, please Contact Us with the following information:

  • Type of film or effect required
  • Is the glazing a single or double glazed unit
  • Is there a kite mark on the glass
  • Windows or conservatory roof panels
  • Which way are the windows facing (North, South, West, East)

On the whole, 99% of our products are compatible with all types of glass, whether single panes or double glazed units. However, when it comes to solar control films, especially the darker ones, glass compatibility is very important. We have therefore added a Specifications tab to all our solar control products, and the coloured vinyl products, to inform our customer before they select a film, and to ensure that it suits their particular type of glazing.

One thing to bear in mind is that once applied, any film will alter the specification of safety glazing. Window film will add a protective layer to the glass preventing it from shattering when broken. In some buildings, toughened glass is specified as it is designed to break safely under impact, and adding a film would compromise this quality. Make sure that you are not compromising a buildings' health and safety requirements by applying window film.

It is also recommended to check the glass or window manufacturer's datasheet as applying film could void your warranty.

Frosted, Patterned & Decorative Films

These types of film have no or little solar control quality and as such are not manufactured or designed to reject or absorb heat. They are therefore suitable for all types of glazing, and can be applied to part or the whole of the glazing. 

Safety & Security Films

Safety and security film, when clear, are suitable for all types of glazing. Please check the compatibility information for combination solar and safety films. It is critical that the glass is not cracked or damaged when applying safety or security films as they are thicker and therefore require more force during the application process.

Solar Control Films

Solar control films are designed to control excess UV, visible light, glare and heat. It is important that you check the glass compatibility information before ordering any solar film, especially for double glazed units.

Coloured Vinyl Films

Coloured vinyls, especially dark coloured ones can absorb heat and therefore should only be applied on appropriate glass as indicated in the product's Specifications tab. The material is very durable so alternatively vinyl films can be applied externally and a bead of silicone used to seal the edges.


Is window film suitable for double glazed units?

Great care must be taken when selecting a solar film, especially the darker ones, for a double glazed unit. It is also worth checking the manufacturer's recommendations as you could void the warranty by applying a film. As a rule, if the pane of glass you are applying the film to is toughened, then most films are suitable as toughened or tempered glass can withstand much higher temperatures than float glass. As an alternative, external films can sometimes be used. External films are much more efficient on double glazed units as they help prevent the heat building up and getting trapped between the panes.

Will window film crack the glass?

Thermal shock occurs when excess heat is combined with poorly built or damaged double glazed units made of float glass, which is why it is important to check the product's specifications and to not apply dark films on double glazed units not made with toughened glass. Float glass has a lower resistance to heat than toughened or tempered glass, and edges are particularly prone to damage during manufacturing and installation, which can exacerbate potential failure. The act of applying the film can also cause any glass to crack if it is already damaged, or if the glass is not held properly within the frame (poor putty). Special care should be taken when applying thick safety or security film where a lot of downward force is required. 

What is thermal shock?

Thermal shock or thermal stress occurs when an area of the pane is hotter than an adjacent area. In some cases, the extra stress will cause the glass to crack. Different types of glass react differently to heat, and by far the most resilient is toughened (or tempered glass), which is used on oven doors for example and will sustain high temperatures.

The edge quality of the glass plays a huge part, and damaged or rough edges will endure less stress than glass which has been cut cleanly. This problem is often hidden inside the frame and applying a solar film to the glass is enough to cause these cracks to spread due to higher heat absorption. Should also be considered the age and material of the window or glazing frame.
Other causes of thermal stress include:

  • Shading caused by large stickers, walls, trees etc.
  • Drapes or curtains close to the glass.
  • Intense reflection, from snow or from the sea for example.
  • Quick changes in temperature from air-conditioning, hot air vents, the rising sun etc.
  • Poor glazing construction, and or poor window installation.
  • Damaged edges on the glass.
  • Small existing cracks hidden within the frame.

Can I apply window film to old windows?

Extra care must be taken when applying film to old windows especially if the putty holding the glass within the frame is missing or brittle. Older glass can be very thin and more fragile as a result. Never apply film to glass which is already cracked.