Glass in a watch: what is its significance?

The glass in a watch, although often overlooked at first, plays a key role in the durability, appearance and functionality of our timepiece. Choosing the right glass can have a big impact on the comfort of the watch and its aesthetics. In this article, we will take a look at the different types of watch glass, understand what their advantages and disadvantages are, and suggest what to look for when choosing the best solution for your watch. Whether you’re a watch lover, a collector, or just looking for the perfect timepiece for everyday use, this guide will help you make an informed decision.

Sapphire glass

Sapphire glass is a synthetic material of the highest hardness, used in watches for its extraordinary scratch resistance. It owes its strength to corundum, the mineral from which synthetic sapphire is produced. It is one of the hardest materials in the world, ranking right after diamond and having the 9th grade on the Mohs scale. Thanks to this, watches with sapphire glass are almost completely scratch-resistant, and their dials retain pristine transparency even after many years of use. With a transparency of as much as 85%, sapphire glass definitely stands out from other materials used in watches.

The only drawback of sapphire glass is its brittleness, which means that despite its great scratch resistance, it can break if struck. This type of glass has mainly Swiss men’s watches top-of-the-line or timepieces by Rolex.

Mineral glass

Mineral glass is the most popular type of glass used in watches, especially in mid- and high-end models. It is characterized by medium scratch resistance, having a Mohs rating of 4, meaning that it is less resistant to scratches than sapphire glass, but is superior to plastic glass in this regard. Its big advantage is good shatter resistance, which it owes to its higher flexibility compared to hard sapphire glass. The cost of manufacturing and replacing mineral glass is higher than its plastic counterparts, but it is still the optimal solution for everyday wearable watches, offering the right balance between durability and cost. Thanks to its versatility, mineral glass is a popular choice for users looking for a practical and aesthetically pleasing timepiece.

Hardened mineral glass

Hardened mineral glass, also known as Hardlex, is a reinforced mineral glass that has been further hardened to increase its resistance to scratches and mechanical damage. Thanks to the hardening process, Hardlex glass retains its natural elasticity, making it less prone to breakage than traditional mineral glass. At the same time, it offers higher scratch resistance, making it an ideal choice for sports watches, including models designed for divers, where durability and reliability are key.

Watch manufacturers such as Seiko (especially in the Automatic series), Vostok Europe, Festina and Adriatica often choose Hardlex glass for its excellent protective properties and longevity.

Hesalite glass

Hesalite glass, made from hardened and purified polypropylene, has the lowest scratch resistance of all types of watch glass, ranking 1-2 on the Mohs scale. Often referred to as plastic glass, however, it has a number of advantages that make it an attractive choice for many users. Its main advantage is that its surface can be easily polished to remove minor scratches. In addition, due to its high elasticity, hessalite glass is more resistant to impact compared to harder glasses such as sapphire or mineral.

The cost of producing hesalite glass is relatively low, which translates into lower prices for watches equipped with this type of glass. For this reason, it is often used in sports and everyday models, such as some watches from the Casio Sport series, stylish Zeppelin models and lightweight Timex Ironman timepieces. The choice between hessalite and mineral glass depends on the individual needs of the wearer – hessalite offers greater flexibility and lower cost, while mineral glass provides better scratch resistance.
Many followers of luxury watchmaking choose such solutions as the men’s Franck Muller watch with sapphire glass. However, there are other solutions available on the market, differing in price, shatter resistance and scratch resistance.