Did you know that tempered glass is four times stronger than annealed glass? The main reason why tempered glass is much safer and stronger than standard glass is that it’s made using a slower cooling process. A slower cooling process helps the glass break in a “safe way” by shattering into many small pieces versus the large jagged chunks of regular glass. How can you tell if your mirrors are tempered? Examine the edges because tempering requires extra processing, the edges of a tempered mirror are usually completely smooth. Glass is a brittle material. Unlike other ductile materials (steel and aluminum), glass failure is often sudden and without warning.