What is the difference between thermal and chemical strengthening?

Thermal strengthening generally requires glass at least 2.0 mm thick. At 2.0 mm, only heat strengthening is available, while full tempering normally requires 3.0 mm or more. Thermally tempered glass breaks into relatively blunt fragments, while chemically strengthened glass can still break into sharp pieces. Thermal strength is evaluated using impact fragmentation and ball-drop tests, while chemical strengthening can also be quantified using CS and DOL stress data.