Window films

History

Window films on building glazing have been in use since the 1960s. Initially, the films were used solely to control the build-up of solar heat inside buildings. While still permitting through-vision, the films reflected solar radiation, creating a cooler indoor climate.

Moving into the 1970s, when energy was at a premium, a new window film function began to emerge: advanced polyester films with insulating properties could help prevent the loss of heat from the inside of the building during colder months. By absorbing and re-radiating infrared heat, these films were installed to increase heat retention, thus saving on energy bills.

Since then, the range of window film products has kept developing and improving, both in terms of functionality, quality and longevity. When specified, installed and maintained correctly, high-performance window films can now be employed to overcome a variety of glazing-related challenges. These include heat gain, glare reduction, UV protection, safety, security, privacy, appearance, cleaning, and energy efficiency.

Applications

Window films and coatings are specified and bought by architects, facilities managers and clients responsible for glazing performance both in multi-storey public buildings – schools, colleges, hospitals, libraries, council offices – and in private housing.

In commercial offices, using window films to reduce glare and heat gain can have a positive effect on staff productivity, whilst in a retail environment, UV-filtering and tinted window films help reduce fading in fabrics and soft furnishings.

There is also a sizeable market for purely decorative/privacy window films, fitted by private individuals in DIY projects.

Below are some of the common and less well-known functions of speciality window films:

Heat gain reduction

Compared to untreated glass, specialist window films can reduce unwanted solar heat in a building by as much as 89%. This in turn reduces the need for cooling systems.

Heat loss reduction

Insulating and low-E window films help prevent the transfer of heat from the inside of the glass to the outside, which reduces heating costs, increases energy efficiency, and contributes to the reduction of the building’s carbon footprint.

Glare reduction

Anti-glare window films reduce glare from direct sunlight, as well as reflections from water, snow or the glazing on surrounding buildings. It can contribute to a better working environment and higher productivity, for example when working in front of a screen.

UV protection

UV protective films can block up to 99% of UV rays, reducing solar heat gain and protecting furnishings and retail stock from fading. Window films have also been developed to filter out infrared radiation.

Glazing appearance

Aside from its technical functions, window films can be used to change the appearance of the glass in anything from a domestic front door to an entire façade. See Finish and appearance below for some of the options.

Manifestation

Where large expanses of glass are installed, there is a legal requirement for small markings to be added to the glass. This makes the glazing easier to spot, which helps prevent accidents. The Glass and Glazing Federation provides regulations for the appearance and placement of such manifestations.

Branding

In commercial environments, window films can be used to display logos, graphics and elaborate designs to enhance a company’s image.

Privacy issues

Obscure and black-out window films can be used to create private spaces in offices and domestic properties.

Graffiti protection

Anti-graffiti window films can be fitted in problem areas. These films either make it easy to remove the graffiti, or if cleaning is impossible, they can be removed and replaced more cheaply and easily than the glass itself.

Electromagnetic signal attenuation

Metallised window films window films have been known to cause electromagnetic interference and radio-frequency disruption, which can be useful for anti-surveillance and data/WiFi protection purposes.

Shatter-proofing

Safety window films do not prevent glass from being broken, but will stop it from shattering into hazardous, flying and falling shards by holding the broken pane together in one piece.

Anti-intruder

Whilst security window films cannot altogether prevent intrusion into a building, they can delay and complicate the process for would-be vandals and looters.

Blast protection

Anti-bomb-blast window films are really just another form of shatter-proofing (or fragment retention) films. In the event of an explosion, hurricane or earthquake, they hold the glass together and prevent injury by flying shards.

Nickel sulphide inclusion

NiS inclusions in older toughened/tempered glass have been shown, in some instances, to result in material failure. Some window films have been designed specifically to control and counteract this problem.

Finish and appearance

Window films can be designed to look as unobtrusive as possible – virtually indistinguishable from bare glass – or to have decorative qualities that complement architectural designs and interiors.

Clear, semi-transparent, frosted or opaque films can be chosen according to application, can be plain or patterned, or designed to replicated leaded and stained glass. Typical colours and tints include bronze, grey, blue, gold and amber.

Accreditation

Window film manufacturers test their products to establish individual performance and ensure durability. There are several standards to which products can be tested. Commonly used standards include EN 12600 (safety), EN 356 (security) and ISO 16933 (blast).

EN 12600 has superseded BS 6206 as a European-wide performance standard for impact safety film for glass. The classifications within this standard (in order of highest performance) are Class 1B1, Class 2B2 and Class 3B3.

After extensive collaboration within the industry, the International Window Films Association expects the first official industry-wide product standards to be released during 2012.

Installation

Decorative window films for domestic use are often installed by the homeowners themselves. However, the film can easily become contaminated, which can lead to decreased performance. For large-expanse or commercial glazing, using a professional installer will ensure successful application of the films.

Composition and manufacture

Whilst window films initially had a reputation for being little more than sticky-back plastic, the technology has come a long way in the past 30 years. Modern window films can have as many as eight layers, and the manufacturing process itself can involve more than a handful of distinct processes.

These processes may include colouring, coating, metallising, sputtering (a more precise and time-consuming form of metallising) and laminating.

Commonly, a window film composite will include one or more layers of the film itself (most often polyester); low- or zero-distortion adhesive for sticking the film to the glass; dyes, tints, metals, UV-inhibitors or other components according to the film’s function; a scratch-resistant coating and a protective release liner that covers the adhesive up until the time of installation.

Maintenance

Directly after installation, some window films may appear hazy or have small pockets of moisture between the film and the glass. These are common result of the bonding process, and will disappear as soon as the window film is fully cured.

Under normal circumstances, window films and coatings will require no more maintenance than a normal window-cleaning routine.

Pricing

In a retrofit situation, or when dealing with a specific building performance issue, the fitting of window films can be an inexpensive alternative to wholesale replacement of the glass itself. Domestic window films for DIY installation can cost £10 or less per linear metre, whilst the cost of high-quality commercial installation will vary greatly depending on the product, the contractor and the application itself.