The actual answer is Borosilicate glass.
Borosilicate glass has a lot of brand names: Pyrex is the most well known (a product of Dow Corning) but as the material itself is not subject to copyright there are more than a few other names: Bomex, Pallex, and a few others. But in the end they are all Borosilicate glass, from the lowliest test tube to the fanciest distillation equipment.
Why Borosilicate glass? The answer is that borosilicate glass is very resitant to heat. Its not that it doesn’t get hot when heated, but rather when heated it does not expand like other types of glass. If another type of glass was used the expansion from heating would result in the labware shattering.
This is not to say that borosilicate glass is not immune to the effects of flame. In fact you really should not expose glass labware to direct flame if you can avoid it. Use a hot plate, or seperate the flame from the glass with a ceramic pad.
Borosilcate glass is highly valued for its lack of expansion when heating – in fact higher-end reflecting telescopes make the mirrors out of borosilicate glass because the low expansion means the sensitive surface of the mirror will not change as the telescope goes from a warm indoors to a cold winter’s night.
So why do they make labware out of glass at all? Why not some other material? Well the main reason is visbility – when doing labwork you need to see what is happening in the glassware wether you need to see it to measure it or to observe the reaction taking place. The secondary answers are; metal won’t react well with acids, cermics need to be too thick to heat quickly, plastic doesn’t heat well, scratches, and is bad with some checmicals (not that they don’t make plastic labware).
So back to the glass – some often ask us if it matters if the glass is made of the brand Pyrex or not. the answer is: it depends, but probably not.
You see, all glass labware might be made of the same glass (branded or not) but not all glass labware is constructed the same. A 500ml beaker from a cheap brand might have thinner glass than a ‘name’ brand. Other factors that enter labware prices are: calibration (how much effort did they spend make sure the markings are accurate), labelling (do the markings stay on the glassware? not always!) design (some labware may not have a rolled top to preventing chipping or lack a pouring spout in certain beakers) all labware is a compromise of features vs. price somewhere. But whatever they do with the design, they will be using borosilicate glass.
Want to buy labware?