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Float Glass vs. Flat Glass vs. Plate Glass vs. Sheet Glass

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The Case of the Definite Definitions


Hi Glass Detective,

Could you please clarify this for me—are the terms float glass, flat glass, plate glass and sheet glass used somewhat interchangeably?

Kind regards,

Gagan M.
United Kingdom


Dear Gagan,

Thank you for making contact with the Glass Detective with your questions regarding what I will refer to as “glass nomenclature”. By the way, has a Glass Dictionary which you may want to take a look at after we have tried to address your questions with this response. Please be aware that not everyone will be in total agreement with my answers, but I feel that for what you want to know, we are going to end up on solid ground. Let’s call this a brief overview so we don’t offend too many of our “expert” friends. One last thing—I am going to answer your questions not in the order in which you presented them but in an order that I think will be clearer and more helpful.  Here we go!

  1. Flat Glass is a broad term that covers everything from float glass, sheet glass, and patterned glass (rolled glasses), to plate glass. Also, processed/fabricated glass products such as mirrors, window glass, tempered glass, laminated glass, insulating glass, bullet-resistant glass and anything and everything else that started out as a flat piece of glass pretty much falls into the category of “flat glass”. To those who work in the glass industry, pretty much all glass other than automotive glass is considered flat glass. This may seem a little silly because even glass used in vehicles started out as flat glass, but the common differentiation is that glass falls into two categories—flat and automotive. Glassware, vases and all of that other stuff has its own categories and is not included here.
  2. Float Glass is glass that is manufactured on a float line where a molten ribbon of glass is made by “floating” the liquid glass mixture over a bed of molten tin. As it “floats” over the tin and on to a conveyor system of air or ceramic rollers, it slowly cools and forms a long ribbon of (now solid) glass that is cut and packed for shipping. It is called “float glass” because of the process by which it was formed; literally floating the liquid glass over liquid tin and slowly cooling it (referred to as annealing) to become what we commonly call “plate glass.”
  3. Plate Glass was not always produced by the “float process”. Prior to the invention of the float process, plate glass was made by grinding large “plates” or ribbons of rough formed glass until it was clear. Therefore, not all plate glass is float glass, but all float glass is plate glass. However, for all practical purposes, I think it is fair to say that “plate glass” and “float glass” are synonymous.
  4. Sheet Glass is made using a series of rollers that draws the molten glass vertically up out of the mixing tank (where the glass is still a liquid). The glass is rolled up vertically, and then as it is cooling, turned horizontally, for further cooling and processing. Sheet glass has historically been used for thinner “flat glass” products. The sheet process has limitations regarding thickness and overall size as well as clarity but was less expensive than the old plate glass grinding process so it became more commonly used in situations where a thinner, typically lower cost but lower quality glass could be used. Residential windows, desk tops, picture frames and so forth were typically made with sheet glass. However, the float process, which is very efficient, now dominates the market for certain thin flat glass products that used to be made using the sheet process. Float glass is considered by most to be of better visual quality and easier to transport and fabricate than sheet manufactured glass. The float process also allows for much larger sizes for thinner glass products.

I hope this information/explanation is of some value to you and I again thank you for contacting the Glass Detective.

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Lyle Hill

Lyle Hill has been in the glass and metal industry for more than 40 years. In this time he has managed glass retail, contract glazing, mirror, architectural window, window film, and automotive glass businesses throughout America. He obtained an MBA from IIT with a focus on Technology and Engineering Management. Hill is also a columnist for glass industry trade magazines and often called the “face” of the glass industry. He has also authored books including “The Broken Tomato and Other Business Parables,” which is available through Amazon. Find out more about Lyle on Linkedin.

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11 Responses

  1. Hi,

    I have a question I need answered.
    How can you tell the difference between float glass and non-float glass, plate glass and non-plate glass?

    1. Hi Daryl,
      Float glass has what is known as a “tin side”. The tin side is the side of the glass that was “floated” over the bed of molten tin as it flowed out of the oven. There are devices which can indicate which side of a piece of glass was the tin side during the float process. Non-float produced plate glass does not have a tin side because it was not floated over tin. Non-float glass is ground/polished on both sides. Feel free to give us a call if you’d like to discuss further.

  2. Why is there no link to see a page about sheet glass but there is for the other types? I am trying to find out in more detail about how sheet glass was/is made for a report I am writing. Or could you refer me to some other source?

  3. Is a mirror made with a greater tolerance for flatness than standard glass. This is a big debate for the 3D printing community

    1. Thanks for the question Stewart. No, typically mirror glass is not made with a different tolerance for flatness than standard glass.

  4. Hi,
    When you have a triple glazing, is it okay to have the mid-pane as floated glass while the outter panes are thermally toughened?

    1. Hi Emica,
      Thanks for the question! Yes, it’s typically okay to have the mid-pane as floated glass as long as it’s clear and not tinted.

  5. Which is better. I have for large windows 80×92 in my great room. Trouble is evidently they are two panes and moisture has shown up between them. When I replace them I want to do it right. Please give me your advice for replacement.

    1. Hi Dallas,
      I think you’ll find this blog helpful in answering your question:

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