Float Glass vs Tempered Glass (Toughened Glass): Know The Difference!

Civil Engineer / Content Writer

Glass practically acts as a magical material, which has so many different properties, and it can be altered very easily to produce different types of glass. Different processes are carried out on glass, to make it more flexible for different applications. Toughened glass which is also known as tempered glass is a popular type of processed glass. It is nowadays extensively used in high rise buildings. So, there is confusion as to how float glass and tempered glass differ. Here we have tried to given brief information on float glass vs tempered glass.

Courtesy - ND-RC

01. Manufacturing Process

Float Glass

  • The raw materials are melted in a furnace to form molten glass. The molten glass is then passed through the temperature-controlled kiln (annealing lehr) for cooling the glass. In annealing lehr, float glass cools gradually and comes out with uniform thickness and flat surface.

Tempered Glass (Toughened Glass)

  • The normal glass or float is heated in the furnace to a uniform temperature of 620-6500C and then rapidly cooled in the annealing lehr to produce tempered glass.

02. Properties

(a) Strength

Float Glass

  • Annealed Glass has less mechanical strength as compared to toughened glass.

Tempered Glass (Toughened Glass)

  • Toughened glass is four to five times stronger than float glass. Hence it can sustain high wind load or snow load easily.

(b) Thermal Stress

Float Glass

  • Float glass can withstand temperature differential of up to 40 0C. Thus float glass breaks due to excessive thermal stresses.

Tempered Glass (Toughened Glass)

  • Tempered glass can withstand temperature differential of up to 250 0C. It has more resistance to thermal stresses.

(c) Breakage Pattern

Float Glass

  • Upon impact float glass breaks into large sharp pieces. These pieces can cause injuries to people; hence float glass is not used as safety glass.

Tempered Glass (Toughened Glass)

  • Toughened glass breaks into small blunt pieces, which are not harmful. Thus it is widely used as a safety glass.

(d) Fabrication

Float Glass

  • Float glass can be processed to form different types of glass. Different fabrication processes such as cutting, drilling, polishing, etc. can be easily carried out on it.

Tempered Glass (Toughened Glass)

  • Tempered glass cannot be cut or re-sized. All the fabrication processes has to be done before tempering of glass panels.

(e) Optical Distortion

Float Glass

  • Float glass is free from any type of optical distortions and thus provides a clear vision.

Tempered Glass (Toughened Glass)

  • Due to tempering, there are some optical distortions on the surface of the glass, which provide a little hazy and unclear vision.

03. Cost

Float Glass

  • It is less expensive as compared to toughened glass.

Tempered Glass (Toughened Glass)

  • Tempered glass is expensive than float glass.

Special Comments

  • Float glass is most widely used glass in doors and windows. In applications when there is prevalence of high wind loads, snow loads, etc. then tempered glass must be used. Nowadays, it is compulsory to use tempered glass in high rise buildings.
  • From the above comparison of float glass vs tempered glass, the user needs to make a judicial choice.

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