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Insulation is measured in U-Values, the lower the figure the better the insulation.


There are various components used in the construction of double glazed units to obtain the required U-Values. Clear Glass, Emissivity glass, inert insulating gases and spacer between the glasses.


Example: Calculated U cog Value (BSEN 8990)


Unit Construction: 4mm Clear Glass/ 4mm Cavity, Air Filled/ 4mm Clear Glass - U-Value 3.7


Unit Construction: 4mm Emissivity glass/ 4mm Cavity, gas filled/ 4mm clear glass - U-Value 1.9


Single glazing has a U-Value of 5.8 and it can readily be seen that 3.7 is an improvement on 5.8 and 1.9 is a significant improvement on 3.7.


The use of emissivity glass to reflect back into room the long wave radiation or heat and selected insulating gas is required to achieve the selected U-Value.


The Example above with U-Value 1.9 is an example of Slimlite Self Cleaning Double Glazed Unit with 5mm perimeter seal. It is possible to lower this U-Value with different insulating gases, and cavities.



Heat loss or gain is affected by more than one factor such as convection, radiance, conduction and is generally reflected as a U-Value or measure of insulation in double glazing which is one of the most important factors in a window of a reasonable size.


A single glazed window is sometimes referred to as a “Thermal Hole”. It is considered that single glazed windows lose around one third or 33% of its heat in the average house. Payback time currently for high insulation double glazed units is estimated at around 5 years depending on cost of units and cost of energy. Future energy costs are a major concern and insulation today is one of the most important factors.


A recent commissioned report claims that since de-regulation of prices in 2002 and from 2002 to 2005 average energy prices have risen by about 60% more than inflation.




Convection is one of the major heat loses relative to a window which is single glazed when it is cold outside and reasonable warm inside.


The warm internal air contacting the cold glass becomes heavier, and drops downwards at a speed of around two metres per second depending on relative temperatures, causing a perpetual expensive heat loss and generally felt as a draught around the legs and feet. 
It is considered that a one degree increase in temperature in a room at comfort level will increase energy costs by 2%.


The use of high insulation Slimlite Self Cleaning Double Glazed Units where the inner pane is warmer will substantially slow down convection and improve the comfort zone.




Everybody knows that an electric fire provides radiant heat which they can feel on their body but more receptive on the face.

Radiant transfer in respect of glass occurs when the warm internal air contacts the cold single glass in a window and radiates or transfers heat outwards through the glass at a constant rate.


Low emissivity glass used in the construction of a double glazed unit reflects the long wave radiation or heat back into the room and therefore reduces the radiant heat going out through the glass.




Conduction is the transfer or movement of heat along or through a material or a gas. For example a metal cooking pan with a solid metal handle has a high conductivity and therefore the handle could be too hot to touch when cooking.


A window construction should use low conductive material and particularly a double glazed unit which forms the largest area normally in a window. All the material in a window will conduct heat or cold depending on the conductivity of each material and a double glazed unit has a major contribution to the insulation factor.


Slimlite  Self Cleaning Double Glazed Units constructed with warm edge spacer to increase the U-Value, low emissivity glass to reflect the heat back into the room and low conductive inert gas ensure that the maximum possible insulation is obtained by utilising and maximising the latest technology to reduce the heat loss by convection, radiance and conduction.

The unique small cavity and small perimeter seal in Slimlite provides the best possible insulation available today.