Apple has pushed the use of sapphire in its iPhone camera lenses as a big selling point since it was introduced in the iPhone 5S. But a new YouTube video shows that it isn’t as durable as the sapphire used in watch faces.

According to JerryRigEverything, a YouTube channel dedicated to testing the durability of different products, Apple is likely saving on manufacturing costs by using a sapphire laminate on top of regular glass in it iPhone lenses.

The video shows Apple’s lens cover scratching from a level 6 pick (on the Mohs scale of mineral hardness), whereas the sapphire of a Tissot watch face only scratches once a level 8 pick is used.

Tests carried out using a XRF machine and an electron microscope prove that pure sapphire isn’t used in the iPhone lenses. It also confirms that they don't contain pure sapphire.

JerryRigEverything asks the question “How impure can your sapphire be, and still call it sapphire?" There's also the issue of whether the sapphire display on the stainless steel Apple Watch also uses a laminate, and, if so, is the device less durable than the marketing suggests.

The video does show that the iPhone 7 sapphire lens cover has the same durability as the iPhone 6, iPhone 5, and iPhone SE. And it’s worth pointing out that the lenses are still fairly scratch resistant, just not as much as Apple makes out.