What material is the crystal, Ion-X Glass or sapphire?

What material is used to make the Apple Watch face? Most Apple Watch models feature a machined and polished single crystal of sapphire comprising the watch face. Sapphire is the hardest transparent material on Earth besides diamond. The Sport collection features Ion-X glass, which is chemically strengthened glass.

There is some confusion, and I’m not even convinced the website has it correct because it suggests sapphire back which is almost certainly wrong. Please refer to the example specification in page https://www.apple.com/shop/buy-watch/apple-watch/space-gray-aluminum-black-sport-band?preSelect=false&product=MU662LL/A&step=detail#

Series 4 (GPS) Features

• Space Gray aluminum case
• Built-in GPS,

[snip for brevity]

Ion-X strengthened glass

Sapphire crystal and ceramic back

[snip]

And in the stainless version

• Sapphire crystal glass
• Sapphire crystal and ceramic back

Not strictly correct in the current models. At least in Series 3 and Series 4 the aluminum body watches use ion-X and the stainless bodies have sapphire. I forget what they used in the now discontinued earlier versions.

Depending on model you buy.

It was that way in the earlier versions. The gold, ceramic and Hermes also had/have sapphire.