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This is your hub for knowledge and information on windows and doors. Over the years, Fenesta has developed a unique understanding of how they work. This knowledge is shared through this section to help you learn what features and materials enable windows and doors to contribute to your home's comfort

Understanding Glass

Glass is amorphous (non-crystalline) transparent / translucent and is produced by floating molten glass over a bed of a liquid tin, which has a low melting temperature. Float glass is made from a mixture of sand, limestone, soda ash, dolomite, iron oxide and salt cake which are heated to a temperature of 1500 degrees Celsius.

The most common glass used is “Lead Glass” for optical use which has 24% or more lead (PbO) by weight and refractive index of more than 1.545 %.


Float or Annealed Glass

Float glass also called as flat glass is annealed glass (not tempered or heat strengthened) and is produced by controlled cooling to prevent residual stress in the glass. Float glass is high quality like sheet glass with good optical clarity like plate glass and can be cut, drilled, machined, edged, bent and polished.

Toughened Glass

Thermally tempered or toughened glass is approx 4 times stronger than annealed glass. Toughened glass is impact resistant and when it is broken it shatters into small, harmless cubes. Toughened glass is made from annealed glass which is heated to 600C and then rapidly cooled. The rapid cooling places internal stresses on the glass which allow it to be strong and break into regular cubes. After the glass is toughened, it is not possible to carry out any alteration like cutting, machining, drilling, sandblasting etc

Heat Strengthened Glass

Heat strengthened glass is subjected to heating / cooling cycle in controlled behaviour and is twice as strong as annealed glass. These glasses also have higher resistance to thermal loads. When broken, the glass fragments break into large pieces and do not result into small fragments like toughened glass, thus allowing it to stay in the opening for a longer duration. Although it is not a safety glass but this breakage pattern prevents the glass from falling and injuring someone This glass cannot be drilled / cut / edged, sandblasting etc.

Frosted Glass

Most commonly used when privacy is required, frosted glass allows light to pass through without clear view. Frosted glass is produced by sand blasting or acid etching float glass.

Insulated or Double Glass

Insulated glass refers to two or more glass sealed around the edges with an air space between the two to form a single unit. The insulating air / gas between the two layers of glass improve the thermal performance of the unit.

Laminated Glass

Laminated glass consists of two or more glass permanently bonded together with one or multiple layer of polyvinylbutyral (PVB). Used most commonly when safety is paramount. When broken, the glass pieces tend to adhere to plastic (PVB) layer. It is recommended to use toughened glass with Lamination. Toughened laminated glass invariably has waviness. This is due to glass process limitation.

Tinted (Colored) Glass

Tinted or light colored glasses are used to for aesthetic appeal or reduce direct glare and providing “soothing feel”. Tinted glass reduces light transmission and therefore proper deliberation should be done before going in for this glass.

Reflective Glass

Reflective glass is glass that has been treated with advanced coatings to reflect heat and radiation from sunlight while allowing the natural light to come in. These glasses cut substantial light and heat and are recommended to be used in double glazing (DG) format.

Borosilicate Glass

Borosilicate glass is a type of heat resistant glass which is most commonly known as Pyrex. It is not affected by changes in temperature due to its low coefficient of thermal expansion. Though sudden temperature fluctuations or rapid heating can cause it to break but instead of shattering like a float glass it is most likely to fracture in one place, making it easier and safer to clean up. Heat resistant glass is less dense than normal glass.

Glass Myth Buster

Glass plays a vital role in the performance of windows and doors. Today there are hundreds of glass options available in the market and glass manufacturers introduce many new shades / options to the customers which either confuses them or make them leave the decision to the interior designer or an architect who are in turn dependent upon the information given by the glass manufacturers.

This section is intended to remove some myths and create a basic understanding of glass and its selection criteria.

  • Myth Buster 1:

    Glass is just filling material in the window pane and does not require any wind load validation. This is not true. Windows & Doors have to pass specified wind load of the city / building. Ask your window provider for wind load chart for glass selection.

  • Myth Buster 2:

    Differential Glass thickness reduces sound. This is not true in way it is being used today. Sound attenuation works on the principle of Mass theory i.e. thicker the glass better the sound insulation properties. The differential glass thickness works when the glass mass multiplies with respect to another. This means when two glasses like 6 & 12, 5 & 10, 4 & 8 is used. It does not have any effect when we use 5&6 or 4&5 etc.

  • Myth Buster 3:

    Double glazing & Triple glazing provide better sound insulation compared to Single Glazing. This is not true. As stated in above part, more the glass mass better is the sound attenuation. This means a Single Glazing (SG) of 0.012m will have better sound insulation over a DG with 0.006+0.012m gap+6!!

  • Myth Buster 4:

    Fenesta Windows will reduce sound by 40dB This is not true always. The sound reduction is based on various factors like noise level outside, type of noise (frequency), type of construction, surrounding etc.