How Can You Tell If PYREX Is Borosilicate


How Can You Tell If PYREX Is Borosilicate

Chances are you just asked Google how you can tell if PYREX is Borosilicate; so, I’m willing to bet you already know the difference between Soda-Lime and Borosilicate glass.  Soda-lime is your standard glass type used in most household applications, while borosilicate is used for more extreme situations such as laboratory tests due to its resistance to thermal shock. 

But, how can you tell if PYREX Borosilicate from home and without a science degree? There are a few different tests you can do on your own, also some that you should not. Let’s go over all of our options and you can decide which is the best for you. 

This article will assume that you own a piece of glass that you are unsure about. If you are shopping, the best way to tell if the product is borosilicate is to read the package

Differentiate By Brand


Pyrex was founded in 1915 and was initially owned by Corning Consumer Products Company. Corning formed World Kitchen, LCC, who later became Corelle Brands. In 1998 Corning rid itself of the Corelle brand and the two split. At the time, they had a licensing contract with Newell Cookware Europe. After Corning dropped the Corelle brand, Newell retained the rights to PYREX. By 2006, Arc International had since acquired PYREX and still owns it in Europe, Africa and the Middle East. Newell continues to make the original quality Borosilicate PYREX. 

After the split in ‘98 Corelle continued to produce “PYREX” under a different brand “pyrex”. The difference in the two companies is the reason why you found your way to this article. Soda-Lime vs. Borosilicate glass. Corelle switched from Borosilicate to Soda-Lime glass and continues to sell the lesser quality soda-lime glass to date. So, if your cookware is spelled in lowercase, it’s soda lime. If it is spelled in upper case then it is European and thus Borosilicate.

Borosilicate Testing Without A Scientist

If you are looking to see if the glass that you already own is Borosilicate then there are a few ways to test it from home. According to the Yale Glass Shop the trick is in the refractive index of 1.474.  If you submerge borosilicate glass into a liquid of a similar refractive index the glass should appear to “disappear”. Three such liquids are Anhydrous glycerol, Dry benzene-methanol mixture, 84:16 (v/v) at room temperature or mineral oil. Yes that's me up there looking awesome. 

Mineral Oil is the best way to go for this test. It is used in cosmetics most commonly and can be found at most drug stores. The Benzene-methanol method requires proper mixing of chemicals and you would have to order Anhydrous glycerol special online. The mineral oil shouldn’t cost you more than $30 to buy a few bottles that would submerge a dish. 

The easiest way to tell if PYREX is Borosilicate is to bring it back to the science class basics and manually measure the density and see if it lines up. I will try and make this as simple as possible:

  1. Measure the length, height and width of your dish
  2. Multiply all three measurements to get your volume in cubic centimetres
  3. Weigh your dish to get its mass
  4. Divide your mass by your volume to get your density. 

If the density of the glass is 2.23 or close you more than likely have borosilicate glass. Soda-lime has a density of 2.52 for comparison sake.

Eyeball It

If you have a dish at home that you want to test you can also try just looking at the hue. If you look at the edge of a dish and it is made out of soda-lime glass it will be a blueish-green hue. If the glass is Borosilicate then you should not see any color.

Lab Tests

There are other methods to see what your glass is made of, but these would fall under the “do not try this at home” category unless you are a seasoned scientist. The first is the flame test. Essentially, you are burning materials to see which color appears. The color is indicative of the materials that are in the test. 

A diamond scratch test can be performed as well. The glass is scratched to determine hardness which can then be used to determine glass type. If you own a diamond drill have at it, but if not I would still recommend a mineral test. 

So, how can you tell if PYREX is borosilicate? The surest way to tell if it is borosilicate is to just buy it that way!  No testing needed. We are the only website in the USA that imports and sells European made Borosilicate PYREX. Check out our selection and let me know if you have any questions, I would love to help you cook safer!