The Ultimate Guide to Watch Crystals: Sapphire vs. Mineral vs. Plexiglass The Ultimate Guide to Watch Crystals: Sapphire vs. Mineral vs. Plexiglass Are you a watch enthusiast wondering what the best material is to protect your dial? The choice of a watch crystal (often called "glass") is crucial, influencing resistance to scratches, impacts, and, naturally, aesthetics. We analyze the five most common types of watch crystals, comparing their features, pros, and cons, to help you make the most informed choice. 1. Plexiglass / Hesalite: The Classic with a Warm Touch Feature Description Material Standard PMMA Scratch Resistance Low Impact Resistance Very High Optical Appearance Warm, slightly soft Key Notes Economical, easily polishable Plexiglass, also known as Hesalite, is an acrylic polymer (PMMA). It is the historical crystal used in many iconic watches. Strength: Its exceptional impact resistance. If struck, it tends to flex or scratch, not shatter. Furthermore, small scratches can be removed with simple polishing. Weakness: Low scratch resistance. It scratches very easily, making it less suitable for rough daily use. PMMA HT (High-Tech): The Evolution of Plexiglass This high-performance variant offers High impact resistance and Medium-low scratch resistance (better than standard Plexiglass). It also resists UV rays and high temperatures, improving its longevity. 2. Mineral Glass (Tempered): The Balance of Cost and Durability Feature Description Material Tempered glass Scratch Resistance Medium Impact Resistance Medium Optical Appearance Transparent, neutral Key Notes Harder but more fragile than Plexiglass Mineral glass is common glass that has undergone a thermal or chemical "tempering" treatment to increase its hardness. It is the most common choice in the mid-range watch segment. Strength: It offers a good compromise between cost, scratch resistance, and impact resistance. The appearance is transparent and neutral, similar to traditional glass. Weakness: Despite being tempered, a sharp impact can still chip or break it, and it is significantly less scratch-resistant than sapphire. Hardlex (Seiko): Proprietary Hardened Mineral A special mention goes to Hardlex, Seiko's proprietary crystal. This is a type of mineral glass that has undergone an additional hardening process to improve its resistance. It offers Medium-high scratch resistance and good impact resistance. 3. Sapphire Crystal (Synthetic Crystal): The Apex of Resistance Feature Description Material Synthetic crystal Scratch Resistance Very High Impact Resistance Medium Optical Appearance Perfectly clear Key Notes Premium, more expensive Sapphire crystal is considered the gold standard in the luxury watch industry. It is not glass in the traditional sense, but a synthetic aluminum oxide crystal ($\text{Al}_2\text{O}_3$). Strength: It has exceptional scratch resistance (9 on the Mohs scale, surpassed only by diamond, which is 10). Scratching a sapphire watch crystal requires an extremely hard material. Weakness: It is more expensive and, despite having medium impact resistance, it is more brittle than Plexiglass. A violent impact on a thin edge can cause it to chip or shatter. Summary Table: Which Crystal Should You Choose? Crystal Type Scratch Resistance Impact Resistance Ideal for... Sapphire Very High Medium Luxury watches, uncompromising daily wear Hardlex / Mineral Medium / Medium-high Medium / Good Sports watches (mid-range), excellent quality/price balance Plexiglass Low Very High Vintage watches, dive/work watches where impacts are frequent Quick FAQ: Common Doubts About Watch Crystals Is Sapphire or Mineral Glass Better? If your priority is the absence of scratches, sapphire is clearly superior. However, if the watch is likely to undergo very violent impacts (where sapphire risks breaking) and you have a smaller budget, mineral glass or Hardlex are a more pragmatic choice. Can Mineral Glass be Replaced with Sapphire? Yes, it is a very common upgrade (modding) to improve the watch's durability. However, the operation requires a qualified watchmaker and a sapphire crystal of the exact size. How to Clean Scratches from Plexiglass? Surface scratches can be removed using a specific plastic polishing paste (like Polywatch) and a soft cloth. This is its great advantage!