Borosilicate glass is known under many names but you’ll probably recognise Pyrex, synonymous with kitchenware. Doesn’t everyone have a clear Pyrex bowl or measuring jug at the back of a cupboard somewhere? Mary Berry sure does!
Pyrex glass is completely non-porous, hypo-allergenic and excellent for body jewellery. It’s an extremely tough glass that reacts well to temperature making it heat resistant ensuring it will not crack with a change in temperature as normal glass could. 
Borosilicate glass is also used in implantable medical grade devices such as prosthetic eyes. Apparently there is just one ocularist (glass eye artist) left in the UK and when he retires, that’s it, finished. Now that would bring a tear to a glass eye. All is not lost as they’re now made from acrylic, but are they as good?
Pyrex glass expanders come in a wonderful selection of colours and designs that can only be created in glass. They are comfortable to wear and will not crack or freeze to the ear!