Chemically strengthened glass is a type of glass that has increased strength as a result of a post-production chemical process. When broken, it still breaks into long, pointed slivers similar to float glass. For this reason it is not considered safety glass and must be laminated if safety glass is required. However, chemically strengthened glass typically has six to eight times the strength of float glass. The most common trademark for this type of glass is Gorilla Glass.

The glass is chemically strengthened through a surface finishing process. The glass is immersed in a bath containing a potassium salt (typically potassium nitrate) at 300 degrees Celsius (572 °F). This causes the sodium ions on the glass surface to be replaced by potassium ions from the bath solution.[1]​.

These potassium ions are larger than sodium ions and therefore fit into the spaces left by the smaller sodium ions when they migrate into the potassium nitrate solution. This substitution of ions causes the surface of the glass to be in a state of compression and the core in compensatory tension. The surface compression of chemically strengthened glass can reach up to 690 MPa "Pascal (unit)").

The strengthening mechanism depends on the fact that the compressive strength of glass is significantly greater than its tensile strength. With both surfaces of the glass already compressed, a certain amount of bending is needed before one of the surfaces can come into tension. More bending is required to achieve tensile strength. The other surface simply experiences increasing compressive stress. But since the compressive strength is much higher, no compression failure is experienced.

There is also a more advanced two-stage process for making chemically strengthened glass, in which the glass article is first immersed in a 450°C (842°F) sodium nitrate bath, which enriches the surface with sodium ions. This leaves more sodium ions in the glass for immersion in potassium nitrate to replace them with potassium ions. In this way, the use of a sodium nitrate bath increases the surface compression potential on the finished article.

Chemical strengthening results in a reinforcement similar to that of tempered glass. However, the process does not use extreme temperature variations and therefore chemically strengthened glass has little to no arcing or warping, optical distortion or warping pattern. This differs from tempered glass, where thin pieces can bow significantly.

Additionally, unlike tempered glass, chemically strengthened glass can be cut after hardening, but loses its additional strength within the approximately 20 mm region of the cut. Similarly, when the surface of chemically strengthened glass is deeply scratched, this area loses its additional strength.