Materials

The materials used in a watch crystal, case and strap: sapphire, mineral, steel, titanium and more.

What a watch is made of largely decides how it ages, how long it lasts and how it feels. The gap between a scratch-proof sapphire crystal and a mineral one that marks easily, or between light titanium and classic steel, shows up quickly in daily wear.

The terms in this section explain crystal, case and strap materials in plain language, so you understand where a watch's price and durability come from.

Acrylic Crystal: Acrylic crystal is a lightweight plastic watch crystal, also called hesalite, that protects the dial. It scratches easily, but those scratches polish straight out, and rather than shattering on impact it tends to flex. It is common on vintage and budget watches.
Hardlex: Hardlex is Seiko's branded hardened mineral crystal. It is tougher and more shatter resistant than ordinary mineral glass, yet softer than sapphire, so keys or grit can still scratch it. You will find it on the Seiko 5 and entry-level Prospex models.
Mineral Crystal: Mineral crystal is a hardened glass fitted over the watch dial. It is far cheaper than sapphire and more resistant to shattering on impact, yet it scratches more readily, rating around 5.5 (roughly 5 to 6) on the Mohs hardness scale against sapphire's 9. Seiko's Hardlex is a branded mineral glass.
Resin: Resin is a tough, lightweight plastic used for watch cases and straps, mostly on affordable and sports watches. It absorbs knocks rather than denting, shrugs off water and sweat, and costs little to make, which is why it defines the classic Casio look.
Sapphire Crystal: Sapphire crystal is the transparent cover over the dial made from synthetic sapphire. It rates a 9 on the Mohs hardness scale, second only to diamond, so it resists scratches far better than mineral glass, although it costs more to produce.
Stainless Steel: Stainless steel is the standard metal for watch cases, usually the surgical-grade 316L alloy. It is corrosion resistant and strong, and it takes both a brushed and a polished finish. It is heavier than titanium and is the default for Orient, Seiko and Citizen cases.
Titanium: Titanium is a case metal much lighter than steel and hypoallergenic, with high strength. It resists corrosion well, but it scratches more readily than steel unless its surface has been hardened. Citizen uses titanium across many of its watches, which is why you meet it so often.