School directors are required to make school windows safe.

 

It is an extra-thin film of polyester ranging from 0.025 to 0.35 mm (25-350 microns) in thickness, comprised of various layers of polyester bonded together with a very thin even layer of adhesive. These layers (generally 2 or 3) contain colouring substances and can be surface treated to give the desired mechanical, thermal and optical properties.

 

Surface treatments give polyester film the desired characteristics.

 

Surface treatments and materials can be combined in different ways to give the colour (neutral, tinted or reflective), thickness, degree of filtration and resistance required for each specific application. There are two main kinds of treatment, vacuum metallizing, and sputtering in which the layer of polyester is bombarded with metal ions.

 

Sputtered film - the metal is heated to boiling point and a static current causes the atoms in the metal to deposit next to each other on the sheet of polyester. Then, using another sheet, the atoms are encapsulated sandwich-fashion to protect them. This treatment makes the film more resistant to solar radiation and more transparent than untreated ones.

 

Metallized film – this undergoes the same process, but  using metallic vapours instead of ionised atoms.