0.25mm HD Premium Real Tempered Glass Screen Protector Protective Film For Smart Mobile Phones ( Nokia Lumia 521 ) 1 Whole Transparency: The protector is 0.25mm thick and made with chemically treated, transparent tempered glass. Surface hardness : 8~9H: The surface of the protector has a hardness of 8-9H, three times stronger than regular PET film. Even shard objects such as knives and keys will not scratch the protector. Anti-Shatter Film: If broken, the protector breaks into small pieces that are not sharp, making it safer than other glass products.