Tempered glass is about four times stronger than “ordinary,” or annealed, glass. And unlike annealed glass, which can shatter into jagged shards when broken,tempered glass fractures into small, relatively harmless pieces.
This is the process that makes the glass four to five times stronger and safer than annealed or untreated glass. As a result, tempered glass is less likely to experience a thermal break. With heat-strengthened glass, the cooling process is slower, which means the compression strength is lower.