Use polyester film 175 microns thick (including adhesive layers of multi-ply) or film with equivalent properties. Consider using 300 micron film for panes over 6 square metres area, or over 8mm thick, or for ground floor windows of over 3 square metres. The specification can be lowered to at least 100 microns if bomb blast net curtains are also used.
The film must be fixed in clean and dust-free conditions. On new windows or areas being re-glazed, apply film to the glass to its extreme edges before fixing the frames. If, however, there is to be extensive building work after installation - in which case dust and debris may cause unacceptable scratching - it may be better to postpone fixing the film until work is complete. In this case the film should be applied as close as possible to the putty of glazing bars with an edge gap of less than 3mm. 5mm can be tolerated along particularly irregular putty edges.
Butt joints are acceptable if the film is insufficiently wide to cover the glass in one piece.
The film cannot be applied to the patterned side of frosted, figured or reeded glass.
With double glazed windows consisting of two separate frames, in which the inner frame can be opened independently of the other, treat both panes. If the inner pane cannot be opened independently, or a sealed unit is fitted, applying film to the inner panel is sufficient. Sometimes inner frames are only lightly fitted; if so, they should be fully secured.