All double glazed units now have the cavity or space between the two panes of glass filled with an inert insulating gas as one of the components to increase insulation values.

The main type of inert insulating or low conductive gas used in standard double glazed units is Argon, but is not the best insulating inert gas. Argon gas is by far the cheapest gas, but does not have the best insulation properties, but is widely used in double glazing manufacture.

To obtain compliance with Building Regulations with standard Double glazing it is necessary to use wide cavities of 12mm to 16mm, which is reflected in the bulky sections of U.P.V.C. windows, necessary to accommodate units of an overall thickness of 20mm to 24mm. The majority of double glazed units are manufactured for this market.

The other inert gases which provide better insulation are much more expensive but provide the best insulation in smaller cavities, as these gases at the wider cavities mentioned above, will cause convection or movement within the wider cavity which effectively transfers cold from the outer pane to the inner pane and therefore loss of insulation.

This convection does not occur in small cavities and therefore very effective in the small cavities of Slimlite Double Glazed Units, which enables them to comply with Building Regulations.

A double glazed unit which has air in the cavity, provides insulation because it is termed as ‘still’ which means there is no convection or movement of air within the cavity and therefore provides insulation. However any cavity wider than 20mm will cause convection and therefore reduction in U-Value.

The best inert gases low conductive insulating gas have varying width of cavity at which convection will not occur in cavities less than 10mm.

The best inert low conductive gases are heavy gases and will only convect lowering insulation where cavities exceed 10mm, and therefore cannot be used in the wider cavities of standard units from 16 to 20mm, which are normally filled with the lighter inexpensive gas argon. This gas and wider cavities are necessary to obtain the insulating values required in Building Regulations Document L England and Document J Scotland.

The combination of the 10mm average perimeter seal depth and overall thickness of the standard unit 20 to 24mm ensures that the window frame must be sufficiently substantial to accommodate this type of unit. This produces visually overall a very bulky window, apart from loss of daylight, more evident in UPVC windows than some timber windows.

Slimlite Double Glazed Units with thin cavities, inert heavier low conductive gases, small perimeter seal depths and U Values to comply with Building Regulations enables window construction with slimmer sections to produce a much more overall visually pleasing window.