The glass is the crystal which covers the dial and protects the dial, hands and movement from dust and water. There are five types of glass used in SEIKO, PULSAR, and LORUS. They are: Acrylic Glass This is a plastic glass also known as a plexi. It is easier to scratch than Hardlex crystal, and reflects more light. Shallow scratches can be buffed out easily. Hardlex Glass This is a toughened mineral crystal glass developed by the SEIKO Watch Corporation, which is highly resistant to knocks and scratching. Hardlex glass is standard in most SEIKO, PULSAR and LORUS models. Mineral Glass A synthetic mineral crystal glass which is highly resistant to knocks and scratches Sapphire Glass A synthetic sapphire glass which is extremely hard to scratch or mark. This glass is second in hardness only to a diamond and is used mostly in the Premium Collection. Sapphlex Glass A new type of glass also developed by and unique to SEIKO. Sapphlex glass is a combination of SEIKO's superior Sapphire and Hardlex glass. The base of the glass is Hardlex and the top is Sapphlex. It is used only in SEIKO sports watches.