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Bifold Door Shop Glossary of Terms

Bifold Door

Bifold doors are glass doors, similar to sliding doors, but with the advantage that the door panels fold back as they slide open, allowing for a larger doorway that is not obstructed by the doors.
Other terms used to describe bifold doors include concertina doors, folding doors, folding sliding doors, bi-folding doors, folding glass doors and sliding folding doors.

Bottom Rebate

The bottom rebate runs along the running tracks to help prevent water penetration, especially essential in areas with severe weather conditions. The small rebate creates a barrier which diverts water away. For illustrations, please see Bi-folding Door Cills.


The bifold door cill is the ledge that runs along the bottom of the door tracks, directing water away from the doorway. More on Bi-folding Door Cills.

Double Glazing

Double glazing is a glazing unit that features two panes of glass divided by a separator. This separator allows for air to remain trapped between the two panes, creating a thermal barrier. For more information see Bi-folding Door Glasses.

Laminated Glass

Laminated glass is a safety and security glass which is made by fusing a sheet of plastic between two sheets of glass. When broken, the sheets of glass remain adhered to the plastic which continues to act as a barrier. For more information see Bifold Door Glasses.

Laminated Profiles

Laminating timber profiles involves splicing the wood into three and then gluing them back together, under high pressure with the wood grains against each other which prevents the frames from twisting, bowing or warping out of shape. Our wooden bifold doors are made using laminated profiles.

Low-E Coating

Low-E stands for low-emittance, and is a coating we apply to our glass that reflects UV rays, keeping heat outside in the hot summer months and inside in the cool winter months. The glass also offers UV protection to prevent fading of soft furnishings and is low-glare. For further information, view our Bi-folding Door Glasses.


The profile refers to the bifold door frame.

RAL colours

RAL is a colour matching system derived from Germany, mainly used for varnishes and powder coatings. For our full range of RAL Colours see our Bi-folding Door Finishes.


Sill is an alternative spelling of Cill.
See Bi-folding Door Cills for more information.

Tempered Glass

Tempered glass is a safety glass that is four times stronger than standard glass. When smashed, tempered glass shatters into small blunt cubes which are unlikely to cause injury. For more information see Bi-folding Door Glasses.

Thermally Broken

Thermally broken frames have had a material with low heat transfer properties placed between the outer frame and inner frame. Thermal breaks are used on metal frames, where heat would usually transfer through the frame easily, resulting in heat loss or gain. Thermally broken bifold doors have a greater energy efficiency and help to control the temperature of your home.


The U-value describes how well an element conducts heat. The U-value indicates the rate of heat transfer through a material, so a lower U-value is better, as it indicates a low transfer of heat, providing better thermal insulation. Our bi-folding door systems range between U-values of 1.4 and 1.79, depending on the material used.