Become an expert on windows

What do you know about casements, mullions and noble gas?

At Inwido, we are passionate about windows, and we are happy to share our knowledge. Below you will find some important window terms that may be of use to those interested in renovation and new-build.

Glazing bars

Glazing bars are used to adapt the style of your windows to the style of your house. There are many styles and alternatives to choose from to reflect as many styles and periods as possible.

Permanent glazing bars

Made of wood, permanent glazing bars are mounted in the exterior window pane of 1.1 and 1.2 Casement windows using a glazing compound seam. They divide the exterior pane into smaller panes.

Removable glazing bars

Made from composite, aluminum or wood, removable glazing bars snap on to the exterior pane of double or triple pane windows. They can be easily removed when you’re washing the windows.

Internal glazing bars

Made from aluminum, internal glazing bars are located between the panes in the window and do not divide the panes. They maintain their appearance year after year, they do not get dirty and are not in the way when you’re washing the windows.

Window air conditioner

Visual division within a window frame. Air currents are controlled by the possibility of opening the window. The term is also used to refer to closed window units within the same frame.

Mullions and transoms

Made from wood or aluminum, mullions and transoms are used to give a one-frame window the impression of a multi-frame window. They are permanent and divide the pane. 

U-Factor values

U-factor value is a measurement of a window’s capacity to insulate. The lower the value, the better a window will insulate. U-factor value is measured in all the materials used in the window, i.e. wood and glass together. Glass always has a better U-factor value than wood. There are several technical solutions used to improve U-factor value. Glass, noble gases and pane spacers are factors considered.

Insulating glass unit

An insulating glass unit is one that is made up of two or three panes with pane spacers between. The unit is sealed and no ventilation exists. To guarantee low U-factor value, triple pane windows are most often recommended. Energy glass has an invisible film on the inside which minimizes heat loss.

Noble gas

Argon and Krypton are used in insulating glass units and improve U-factor value. Both gases are extracted from air and are not dangerous to health. Noble gases insulate better than air.

Pane spacers

Between the panes of insulating glass units there are pane spacers. Composite covered pane spacers can be integrated in order to attain better U-factor values. Information about manufacture date and what materials were used in the manufacture of the insulating glass units can be found on the pane spacers.


On the inside
Condensation on the inside of the window arises when warm and moist room air is cooled on a cold glass surface and takes the form of mist on glass. Reasons can vary from moisture obtained during manufacture to inadequate ventilation within the window unit. Curtain arrangements which are too close to the window or window sills too close to the wall can inhibit air circulation and cause condensation.

On the outside

When a very well insulated window is placed in an unprotected position, or a position where there is high humidity, condensation can arise. Mist on the pane builds up mainly during the night and disappears during the morning. The reason for this is that the pane insulates so well that no warm air is let through to the exterior pane. The result is that the exterior pane can be colder than the cold night air. The high humidity causes temporary condensation on the exterior pane of the window. Normally, this form of condensation occurs during fall and winter because of the contrasts in temperature between day and night. In the morning, the pane becomes warmer and the condensation evaporates. Condensation on the outside is not a sign that a window is faulty. Quite the opposite. It is a sign that a window is insulating extremely well.

Fixed frame

Cannot be opened. An economic alternative when you want a window close to a French door or other large glass opening.

Side hung windows

The traditional Swedish outward opening window with hinges on the sides.

Top hung windows

Same construction as side hung windows but with hinges on the top.

Tilt-and-turn windows

Windows with fittings that make it possible to rotate the window through 180º so that the exterior pane is facing inwards. This is very practical when washing windows.


A measurement of the sound insulating capability of a window. The higher the value, the better the window will insulate sound. Example: an increase from dB Rw 35 to dB Rw 45 will result in a noise reduction of 75 percent.

Module dimension

All our window module dimensions are specified using the required ‘hole in wall’ dimension. The actual dimensions of the frame are slightly smaller to allow for fitting and adjustments. Example: The actual frame measurements of a 1000 x 1000 mm tilt-and-turn window are 980 x 980 mm.


Window and door measurements are always stated in width by height (w x h).  Sizes relate to module measurements. The ‘hole in the wall’ is the size of the module. If unsure, contact your builder/carpenter.

Night vent

Mounted in the upper part of the window frame.