What is Pyrex glass?

Pyrex glass

We explain what Pyrex glass is, its characteristics, composition, advantages and disadvantages of its use

Pyrex glass bowl

What is Pyrex glass?

The Pyrex glass is a special borosilicate glass whose mark (Pyrex) made its appearance in New York City in 1915, manufactured by Corning Glass. It emerged as a material for modern food packaging, also used to store and bake food in the same type of container.

The origin of the word Pyrex has generated certain discrepancies, but it is accepted that it is derived from the best-selling item in the initial moments of its commercialization: a plate in which a cake was baked. This glass makes many materials and laboratory equipment in many forms, such as sheets or plates, tubes, cells, and rods.

These instruments have different sizes, thicknesses and have different applications and uses, which require different degrees of precision, chemical, mechanical and thermal resistance. Likewise, with Pyrex glass, volumetric glass materials (pipettes, burettes, graduated cylinders, etc.) are made.

Its molecules do not react chemically with the liquids it contains, be they acids or bases; therefore, it does not alter the pH of the packed substances either. In the beginning they were considered heavy and expensive as kitchen utensils.

Chemical composition of Pyrex glass

Pyrex glass container

According to the National Institute of Standards and Technology of the United States, all the manufacturers of Pyrex equipment and instruments – such as Corning, the Arc International Pyrex and Pyrex laboratories – have in common that they manufacture it starting from a borosilicate glass that has the following elements chemicals:

Several manufacturers or suppliers of Pyrex glass have standardized the composition as specified below, also in percentage concentration units w / w:

Characteristics and properties of pyrex glass

The following table summarizes the general mechanical, thermal and electrical properties or characteristics that are attributed to Pyrex glass or borosilicate glass:

The chemical composition of Pyrex, its properties and the quality of the processes in its manufacture allow us to summarize the following properties:

  • Chemically, borosilicate glass is resistant to contact with water, the vast majority of acids, halogens, organic solvents, and saline solutions. For this reason, glass flasks and bottles are made from this material.
  • It has high hydrolytic resistance, which is why it supports high temperatures and the repeated thermal stresses to which it is subjected. For example, it is resistant to the consecutive sterilization processes to which it can be subjected with the use of humid heat (autoclave).
  • Because Pyrex has a low coefficient of thermal expansion, it can be used at 500 ° C, but it is recommended that it be for a short time.
  • Its material is homogeneous, pure, and its content of bubbles and inclusions is very low.
  • It is very resistant to shocks.
  • It has a good index of refraction.
  • With regard to optical properties, the ability of pyrex to transmit light in the visible range of the spectrum, close to ultraviolet light, is fully exploited in the area of ​​chemical photometry.

Borosilicate structure

Pyrex glass

The upper image illustrates an ordered structure of silicates, which contrasts with the true amorphous arrangements of pyrex glass.

Viewed from above, it appears to consist of yellow triangles, but they are actually tetrahedra, with a metallic silicon atom in the center and oxygen atoms at their vertices.

Despite the crystalline appearance, molecularly the borosilicate mesh shows disordered patterns; that is, it is an amorphous solid.

Thus, silicate tetrahedra bind to boric oxides (B 2 O 3 ). Boron here is found as a trigonal plane. In other words, they are tetrahedra bonded to flat boron triangles.

However, this disorder – or amorphous structure – allows it to house cations, which reinforce molecular interactions.


  • It is very useful for the manufacture of equipment and glass materials used in chemistry and scientific research laboratories, such as centrifuge tubes, volumetric glassware, pipettes and borosilicate filter discs, all of them standardized according to international quality standards ISO.
  • Conical, spherical, flat, and threaded Pyrex glass joints are also made.
  • Glass substrates are made for dielectric coating, and for making very thin precision lenses and optics.
  • It is used in the aerospace industry, specifically for the manufacture of reflective optical equipment due to its low thermal expansion. Likewise, mirrors for telescopes have been made with the Pyrex.
  • Allows the manufacture of very thick glass containers
  • It is used in the preparation of surfaces used as substrates with sensor function.
  • It is used in the manufacture of instruments and protective covers of high temperatures.
  • It serves as a material for glass artifacts that absorb neutrons.


So far there are very few relevant aspects that can be pointed out as disadvantages of Pyrex glass:

  • From a chemical point of view, it is recognized that Pyrex glass is attacked by hydrofluoric acid, by concentrated and hot phosphoric acid, and by strong alkaline solutions that cause a corrosive effect on it.
  • Pyrex glass manufacturers do not guarantee the stability of the materials when used under different conditions of vacuum and pressure. For this reason, it is essential to take into account the information provided by the manufacturer and follow their instructions to ensure the protection of both the material and the user.
  • There are few reviews of consumer protection bodies with situations related to safety in their use with containers used to bake food after suffering fractures due to blows or falls.

Pyrex glass in the kitchen

In relation to this type of utensils used in the kitchen, several comparative studies have been presented between containers made with borosilicate Pyrex and utensils made with tempered glass with soda lime.

Pyrex has been confirmed to be more resistant to high temperatures, but has less mechanical resistance than tempered glass containers used for the same purpose.

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