Frequently Asked Questions


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

Pilkington UK - Architectural Glass

  1. Pilkington Architectural (Pilkington Planarenquiries only) - Tel: 01744 692000   send e-mail
  2. Pilkington Basingstoke  - Tel:  01256 469 651   send e-mail
  3. Pilkington Birmingham  - Tel: 0121 326 5300   send e-mail
  4. Pilkington Bradford  - Tel: 01274 683 503   send e-mail
  5. Pilkington Gateshead  - Tel: 0191 487 7300   send e-mail
  6. Pilkington Nottingham  - Tel: 01159 400 980   send e-mail
  7. Pilkington Plyglass, Alfreton  - Tel: 01773 520 000   send e-mail
  8. Pilkington Salford  - Tel: 0161 932 8200   send e-mail


What is "Low e" K Glass and how does it benefit the customer?

Low e products, such as the K Glass™ and Optitherm™ ranges are high quality clear float glass with a specially formulated, permanent, transparent Low E coating applied 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.


  • 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  
  • Pilkington K Glass™ can be combined with solar control glasses to offer full energy management solutions 
  • 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 centre 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 centre 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 S1 Plus centre pane has a U value of 1.0 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 satisfy a specific fire rating?

Pilkington Specifire incorporates all the information you need to choose the right product for your application. We recommend that you check with your local authority to see which level of fire resistance is applicable for your project.

Fire resistance is defined in BS 476: Part 20: 1987 as the ability of an element of building construction to withstand exposure to a standard temperature, time and pressure regime without loss of its fire separating function or loadbearing function or both for a given time

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


Pilkington manufacture a range of fire resistant products to match the fire requirements for your project. The Pilkington Specifire programme is available on the website by using the link below.   This will help specify the type of fire rated glass suitable for your application and allows you to download the relevant framing details.


What is the best U value I can achieve using double glazing?

By combining Pilkington K Glass™ OW on surface 4* of an IGU with Pilkington Optitherm™ S1 Plus ultra low-emissivity glass on Surface 2**, a very low Ug value of 0.9 W/m3K can be achieved. Put simply, you can get triple performance with only two panes of glass.

Pilkington K Glass™ OW has always been the ideal choice for clarity. As an advanced form of the original Pilkington K Glass, it provides better light transmission and allows in more free heat from the sun to enable householders to reduce energy usage and save money on heating bills

*the exterior surface of the inside pane

**the interior surface of the outside pane


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 glass should we specify for a south facing conservatory to have solar control but also thermal performance to keep in warm in the cooler months?

To maximise the reduction of solar gain, the ideal position for a solar control glass in a double glazing unit is the outer pane

Pilkington Suncool™ One is a neutral product, which provides excellent solar control, keeping your conservatory cooler on hot days. The added benefit is its thermal coating, so during cooler weather, it works by reducing the amount of heat escaping from the room.

If a tinted product is preferred, you could choose from the Pilkington Optifloat™ Tint range, which is available is grey, blue, bronze or green. 

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 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.

Pilkington K Glass™ and K Glass™ S and Optitherm™ S1 Plus are not solar control products: however, their presence in a double glazing unit can considerably improve its thermal insulation (reduce the U-Value) over conventional units. The ideal position for these products’ 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.

Better insulation and no cold spots near windows make Pilkington K Glass™, K Glass™ S and Optitherm™ S1 Plus an excellent choice for conservatories, because thanks to a special low emissivity coating on the surface of the glass, it lets 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.  

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™, K Glass™ S and Optitherm™ S1 Plus can be manufactured in both toughened and laminated forms.


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 EN 12600 have to be marked and seen when safety glass has been installed? 

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.

EN 12600 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 no more than the equivalent of 6500mm2 of the original test piece.
  • 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 EN 12600) and it is not possible to pass a 76mm 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 EN 12600 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 EN12150 or BS EN 14449
  • The classification relating to impact test behaviour (Class 1, 2 or 3).
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 6262 Part 4.