Rumors have persisted for weeks that Apple will go with a sapphire crystal display in both of its new iPhone 6 models this September. Apple has said that its decision to go with sapphire crystal pertains to the durability of sapphire crystal when matched up against the current Gorilla Glass display on the iPhone 5s and earlier iPhone models.

Well, the truth is a mixed bag. Sapphire crystal is durable – but under certain circumstances. It surpasses Gorilla Glass in some but doesn’t in others.

A new YouTube video posted by YouTube member Steve Hemmerstoffer shows that the sapphire crystal remains tough in a myriad of circumstances – key scratches, knife cuts, drops on its face, and hammer impacts. As we’ve seen with the first iPhone 6 display video posted by tech blogger Marques Brownlee, the sapphire crystal display will also hold up when bent under your shoe. It seems to be pretty impressive against any other display panel we’ve ever seen.

The problem comes in, however, when the sapphire crystal display is run over by a vehicle. The moment the tire hits the panel, the screen cracks. By the time the car has run over the phone completely and is out of the way, the screen is badly broken. So, the video seems to get our hopes up that sapphire crystal surpasses Gorilla Glass in every way – until we see the end where sapphire crystal meets rubber and fails.

These results are of no surprise to Gorilla Glass manufacturer Corning, who’s gone on record as saying that sapphire crystal (in large amounts) is more fragile than Gorilla Glass. Corning also makes sapphire displays for military purposes, so it seems to know a thing or two about which display is superior.

Thus, expect your sapphire crystal display to hold up in a number of circumstances, but ensure that your iPhone 6 doesn’t fall out of your pocket. If it’s run over by a car, the best you can do is make good on that additional AppleCare protection plan premium.