Untreated Glass

• Regular glass is a very useful substance, but among its limitations are its tendency to shatter into razor-sharp pieces on impact, its tendency to crack upon experiencing sudden changes in temperature (thermal shock), and its low structural strength. Tempered glass and borosilicate glass are special glasses that are made to improve the performance of the material in one or more of these areas.
  
  

Borosilicate Glass

• This special glass is especially resistant to thermal shock, but is also stronger and more durable than regular glass. The trademarked laboratory glassware Pyrex is an example of this type of glass. Borosilicate glass is made by replacing the calcium carbonate component of regular glass with boric oxide.
  
  

Tempered Glass

• Tempered glass is regular glass that has been treated with a thermal or chemical process to make it stronger and more heat-resistant. If broken, it breaks into many small squared-off fragments, making it safer to use in applications such as the side and back windows of passenger vehicles and the glass doors and windows of buildings.
  
  

Differences

• Borosilicate glass has superior thermal shock resistance and a lower thermal expansion factor, which is useful in some special optical uses such as instrument lenses. Tempered glass is better for use in passenger vehicles, as its physical characteristics make it less likely to form shards upon breaking; it also cannot be cut or physically altered once tempered.
  
  

Similarities

• Both types of glass are stronger and more resistant to thermal shock than regular glass.