Frequently Asked Questions


How do I contact my nearest Pilkington UK branch or local glass supplier?

Pilkington UK - Architectural Glass

 Pilkington Architectural (Pilkington Planar™ enquiries only) - Tel: 01744 692000   send e-mail
2   Pilkington AG, Barnsley - Tel: 01226 356500   send e-mail
3   Pilkington Basingstoke  - Tel:  01256 469 651   send e-mail
4   Pilkington Birmingham  - Tel: 0121 326 5300   send e-mail
5   Pilkington Bradford  - Tel: 01274 683 503   send e-mail
6   Pilkington Bristol  - Tel: 01179 001 300   send e-mail
7   Pilkington Cumbernauld  - Tel: 01236 728 298   send e-mail
8   Pilkington Gateshead  - Tel: 0191 487 7300   send e-mail
9   Pilkington Nottingham  - Tel: 01159 400 980   send e-mail
10  Pilkington Plyglass, Alfreton  - Tel: 01773 520 000   send e-mail
11  Pilkington Salford  - Tel: 0161 932 8200   send e-mail


What is Pilkington K Glass™ and how does it benefit the customer?

Pilkington K Glass™ is a high quality clear float glass with a specially formulated, permanent, transparent Low E coating applied pyrolitically to one surface during glass manufacture.

The coating allows the sun's energy to enter the building and when incorporated into insulating units, significantly reduces heat loss. It is usually used in insulating glass units with the coated surface facing the cavity.

Pilkington K Glass™

  • Improve thermal insulation (lower heat losses), thus saving energy and reducing CO2 emissions. 
  • Retain warmth in rooms, increasing occupant comfort 
  • Reduce heating bills 
  • Reduce condensation, cold spots and downdraughts near windows, increasing useful floor space 
  • Available as toughened or laminated options for safety and security 
  • A true low emissivity glass (emissivity less than 0.2) 
  • Specifically designed to reduce heat loss through a window 
  • Low emissivity coating allows the free short wave energy from the sun to enter the building, but acts as a barrier to the escape of expensive long wave energy from internal heat sources 
  • Excellent thermal insulation characteristics, reducing heat loss by 30% over ordinary double glazing 
  • Windows can become a positive contributor to a building's heating needs by optimising 'free' heat from the sun 
  • Can be used in Pilkington Insulight™ 
  • Pilkington Insulight™, incorporating Pilkington K Glass™ can achieve U values of 1.5 W/m2
  • Pilkington K Glass™ can be combined with solar control glasses to offer full energy management solutions 
  • Neutral colour in transmission and reflection
  • Also available on low iron glass substrate as Pilkington K Glass OW for increased light transmittance and g value


What is the U Value of a typical unit?

Heat loss is normally measured by the thermal transmittance or U value, usually expressed in W/m2K. In its most basic terms, the lower the U value, the greater the thermal insulation.  U values for insulating glass units are determined in accordance with BS EN 673. 

An insulating glass unit comprising 4 mm Pilkington Optifloat Clear outer pane, 16 mm argon gas-filled cavity and 4 mm Pilkington K Glass inner pane has a U value of 1.5 W/m2K. 

An insulating glass unit comprising 4 mm Pilkington Optifloat Clear outer pane, 16 mm argon gas-filled cavity and 4 mm Pilkington K Glass S inner pane has a U value of 1.2 W/m2K.

An insulating glass unit comprising 4 mm Pilkington Optifloat Clear outer pane, 16 mm argon gas-filled cavity and 4 mm Pilkington Optitherm S3 inner pane has a U value of 1.1 W/m2K. 

An insulating glass unit comprising 4 mm Pilkington Optifloat Clear outer pane, 16 mm argon gas-filled cavity and 4 mm Pilkington Optitherm S1 Plus inner pane has a U value of 1.0 W/m2K. 

Pilkington energiKare Advantage 0.9, a new innovation in double glazing, has a U value of 0.9 W/m2K.

For more information on our range of products for thermal insulation, please click here.

U values for any of our double and triple glazing combinations can be calculated using our Spectrum online tool.  Registration is free and easy.  Please click here to register.


Which glass would I need to use to give me 30-min integrity or integrity and insulation?

Click on the following links to view the Fire Performance Tables for:

Timber Frames 
Steel Frames

The Pilkington Specifire incorporates all the information you need to choose the right product for your application. By answering a series of questions you are taken to a screen highlighting the product, its properties and performance and details of its fire testing pedigree. The disc also incorporates copies of all Pilkington’s fire test summaries and details of compatible sealant materials. Click here to use the Pilkington Specifire.


What thickness of glass would I need for a glass floor 1m sq. fully supported (all four edges) with a possible loading figure of 1.5 kn./m sq. in a domestic situation?

Glass Floors and Stairtreads

The following should be treated as general guidance only.

The uniformly distributed and concentrated design loads for floors and stairtreads should be determined from BS6399: Part 1.

The preferred general glass specification is Pilkington Optilam™ incorporating thick annealed Pilkington Optifloat™ suitably supported along all four edges.

Approximately 1m2 is usually considered to be a practical maximum area for each pane of glass due to handling considerations.

The table is based on a 1m2 floor pane and a 300 x 1500mm stairtread pane, and relates the design loading to the glass ply thicknesses for each Pilkington Optilam™ pane.

The glasses should be installed with the thicker glass ply uppermost.

Consideration must be given to the surface finish of the glass
– Glass ply thicknesses for floors and stairtreads using Pilkington Optilam™
(Based on floor pane 1m2 in area, and stairtread measuring 300 x 1500mm)

 Intensity of Distributed Load (kN/m2)    Concentrated Load (kN) Pilkington Safety Laminated Glass Configuration (mm + mm)     Typical Usage







19 + 10

25 + 15

25 + 25


Dance Floor


 4.0      4.0  25 + 10  Stairtread


What glass would need to be specified for a conservatory south facing and also incorporating Pilkington K Glass™ in the double glazed unit?

The Pilkington Optifloat™ Tinted (formerly known as Pilkington Antisun™) range has long been an industry standard for low-to-medium performance glass with the Pilkington Suncool™ range suiting high performance needs. The Pilkington Eclipse Advantage™ range fits between the two.

To maximise the reduction of solar gain, the ideal position for a solar control glass (e.g. Pilkington Optifloat™ Tinted) in a double glazing unit is the outer pane. Pilkington K Glass™ is not a solar control glass: however, its presence in a double glazing unit can considerably improve its thermal insulation (reduce the U-Value) over conventional units. The ideal position for the Pilkington K Glass™ low emissivity coating is on the inner pane facing the cavity. Hence, if the requirements are for reduced solar gain and improved thermal insulation, both types of glass can be combined in one unit. Both Pilkington K Glass™ and Pilkington Optifloat™ Tinted are available in toughened and laminated form.

Better insulation and no cold spots near windows make Pilkington K Glass™ an excellent choice for conservatories, because thanks to a special low emissivity coating on the surface of the glass, it let's the sun's rays through, but reflects heat from fires and radiators back into your home - heat which ordinary double gazing allows to escape. In fact it will typically keep an unheated conservatory much more comfortable for a greater part of the year than ordinary double glazing, allowing the occupier to make the most of the conservatory all year round. The effect of suppressing the insulating properties of Pilkington K Glass™ double glazing.

This in turn has the knock on effect of not only lowering household bills, but also helps the environment by reducing the amount of heating needed to keep a house warm. Safety and security issues can also be tackled, as insulating units incorporating Pilkington K Glass™ can be manufactured in both toughened and laminated forms.

An attractive addition to any home, a conservatory requires a lot of hard work in order for it to look great all year round. Self-cleaning glass is the ultimate solution for conservatory owners. A glass roof is a striking feature but must be well maintained in order for it to fulfil its purpose. Pilkington Activ™ Blue and Pilkington Activ SunShade™ Neutral were designed with conservatories in mind and are the perfect self-cleaning and solar control solutions for glass roofs.

Pilkington Activ SunShade Blue is a new product that combines solar control performance with self-cleaning.  When used in an insulating glass unit with an inner pane of Optitherm S1 Plus, the unit can cut out 80% of the sun's heat.


What is the standard thickness of glass for a shop front of X size of double glazed unit?

Generally, display windows (including shop fronts) are exempt from the requirements of Part L of the building regulations and as such are usually glazed with a single pane. The specification of an appropriate glass for shop front applications may depend upon a number of factors, including the size of the pane, how it's supported and the design wind load.

For specific advice on glass for shop fronts, please contact the Pilkington Technical Advisory Service on (01744) 69 2000.


Does the BS6206 have to be marked and seen when safety glass has been installed?

BS 6206 defines the term breaks safely by reference to the outcome of the impact test. 

  • Toughened glass breaks safely if the glass breaks into sufficiently small fragments after impact, I.e. if the weight of the 10 largest crack-free particles weigh less than the equivalent of 6500mm2 of the original sample. 
  • Laminated glass, wired glass and filmed glass are deemed to have broken safely if, after the impact, any glass fragments which fall off are not too large (defined in BS 6206) and it is not possible to pass a 75mm diameter sphere through any opening formed in the glass.

Other glass products used for glazing, e.g. annealed (ordinary) glass, or heat strengthened glass, do not break safely, and can only pass the requirements if they do not break in the test.
The test requires either a standard size or the maximum size of pane available if this is smaller than the standard size. The test specimen size is 865x1930mm.

A safety glass only complies with BS6206 if it is marked as doing so. The standard requires that all installed panels shall be marked to include the following: 

  • An identifiable name or trademark or other mark capable of identification through a suitable source 
  • The type of material 
  • The number of the British Standard, i.e. BS 6206 
  • The classification relating to impact test behaviour (Class A, B or C).

These marks shall be permanent and applied before installation in a position to remain visible after installation. All suppliers of final cut sizes of safety glass should mark the glass in accordance with BS 6206.

BS 6206 has now been superseded and replaced by EN 12600. Marking of safety glass has now changed. Please see BS 6262 Part 4 for requirements or contact the Technical Advisory Service on (01744) 69 2000 for guidance.


What does integrity and insulation mean?

Both relate to fire resistant glazing:


Is defined in BS 476: Part 20: 1987 as, "The ability of a specimen of a separating element to contain a fire to specified criteria of collapse, freedom from holes, cracks and fissures and sustained flaming on the unexposed face.


Is defined in BS 476: Part 20: 1987 as, "The ability of a specimen of a separating element to restrict the temperature rise of the unexposed face to below specified levels". This requires, in a test, that the unexposed face rises on average by no more than 140°C and in any single position by no more than 180°C