Composition testing of what is purportedly a shell for Apple's next-generation iPhone confirms previous reports that the new device will move to 7000-series aluminum, an alloy first introduced to Apple's lineup with the Watch.

The supposed iPhone 6s shell acquired by Unbox Therapy shows high concentrations of zinc, indicative of 7000-series aluminum. Generally speaking, adding zinc — along with magnesium — Â to create 7000-series aluminum results in an alloy that is much harder than the more popular 6000-series, and consequently more difficult to work with.

When the Watch was announced, Apple proudly pointed out that the 7000-series alloy used in the sport models was in fact a custom Apple composition, though it's still not clear exactly what they changed. It's possible that they could've made concessions to make the material easier to handle during manufacturing, for instance, though they claim substantial improvements in strength.

"For Apple Watch Sport, we started with 7000 Series aluminum — the same used in competition bicycles," Apple says on its website. "We altered it to create a new alloy that's just as light, yet even more durable — it's 60 percent stronger than most aluminum, and one-third the density of stainless steel."

While it's not clear whether the alloy used for the iPhone 6s will be exactly the same as the one used for the Watch, the move is likely to make the handsets much stronger. Many users have found that the smoothly-rounded corners of the iPhone 6 and 6 Plus are easy to dent, a charge long leveled at the also-aluminum MacBook lineup.