What Is Tempered Glass for Glass Shower Doors Niles, IL? If you’re like most people, the word tempered glass is probably new to you. However, it’s actually not that difficult to understand what this type of glass is and how it differs from standard glass. Unlike regular annealed glass, tempered glass has been hardened through a process called thermal tempering. It’s approximately four times stronger than annealed glass, making it ideal for use in locations where safety is a concern. If one of your glass shower doors Niles is made from tempered glass panels, you can rest easy knowing that these products won’t create sharp edges if they break—and they rarely do break because tempered glass is so durable.