Window Film (Solar, Privacy & Safety)

Window film is usually a polyester film with a pressure-sensitive adhesive on one side and a scratch-resistant coat on the other. BS EN 15752-1 sets out definitions and performance requirements for adhesive-backed polymeric film used on glass in buildings.

Not every glass suits every film. Dark or reflective films absorb more heat, which can cause thermal stress cracks in some glass, especially large annealed panes or tinted glass. A film-to-glass compatibility check before ordering looks at glass type, size, thickness and whether it is double glazed.

Solar control films reflect or absorb part of the sun's heat before it reaches the room, which helps with overheating in south and west-facing rooms, conservatories and offices. Darker and more reflective films reject more heat, but they also let in less daylight and change the outside appearance.

Many window films block most ultraviolet light, which is one cause of fading in furniture, floors and stock. Visible light and heat also contribute to fading, so film slows fading rather than stopping it. A clear UV film changes the view very little.

One-way mirror films give privacy only when the outside is brighter than the inside. During the day, people outside see a reflection. At night, with lights on indoors, the effect reverses and people can see in, so blinds or a frosted film are needed for night-time privacy.

Frosted and decorative films give privacy while letting daylight through, much like etched or sandblasted glass. They suit bathrooms, front door side panels, ground-floor windows and office partitions, and can be cut into bands, patterns, logos or lettering. They can usually be removed later without damaging the glass.

Safety films hold the pieces together if the glass breaks, reducing the risk of injury from flying or falling shards. Some safety films have been impact tested to BS EN 12600 when applied to glass. Ask for the film's tested class, as performance depends on the film and the glass.

Workplace regulations require windows, glazed doors and transparent partitions to be of safety material or protected against breakage where needed for health or safety. On existing glass in a workplace, a suitable tested safety film is one way of protecting it without replacing the pane.

Security films are thicker than safety films and are designed to delay a break-in by keeping broken glass in the frame. For greater resistance, the film edge can be anchored to the frame with a structural sealant or a mechanical fixing strip, so the whole pane is harder to push in.

On large glass doors and screens in shops and offices, manifestation markings help people see the glass. In England, Approved Document K shows manifestation at two height zones, 850mm–1000mm and 1400mm–1600mm above floor level. Frosted bands, dots or logos in film can provide this.

Film is applied wet, so slight haze or small water pockets are normal at first and clear as the film cures. Curing takes longer in cold, damp weather. Avoid cleaning the filmed glass until the fitter says it has cured, then use a soft cloth and mild soapy water.

The cost of window film depends on the total area, the type of film, the number and size of panes, whether the film is applied inside or outside, any edge anchoring, cut designs or lettering, and access. Large single panes cost less per area than many small panes.