New aluminum alloy isn't to blame for iPhone 6S weight gain

You might notice something's a little different the first time you pick up an iPhone 6S. It's heavier than the iPhone 6. Not massively so, but it's not insignificant, either: both the 6S and the 6S Plus weigh about 11 percent more than last year's models, respectively.

Update: Read the iPhone 6S review.

But where does the extra heft come from? You might suspect that the stronger, aerospace-grade aluminum alloy used in the 6S is to blame, but you'd be wrong. The exact mixture of Apple's customized aluminum alloy is unknown, but the 7000-series alloys are only very slightly more dense than 6000-series mixtures, the type which was reportedly used in the iPhone 6. The difference between the two is the alloying elements: 7000 series is primarily alloyed with zinc, compared to magnesium and silicon in 6000 series aluminum.

New aluminum alloy is just about as dense as before

According to Apple, the aluminum in the 6S Plus only weighs 2 grams more than the aluminum in its predecessor. The aluminum in the 6S weighs a gram less than that in the 6. So, the new aluminum might keep iPhones from bending in half, but it's not to blame for the weight gain.

It turns out the extra heft comes almost solely from that new 3D Touch display. The display assembly now weighs over twice as much as before. In the 6, the display used to weigh 12 grams — it now weighs 29 grams. That's because Apple had to add an entirely new layer to its display assembly to measure pressure. There's a new capacitive pressure sensor built into the backlight of the display; as rumored, it makes the screen slightly thicker and quite a bit heavier.

At the end of the day, the 6S and 6S Plus only weigh 14 and 20 grams more than the models they replace, respectively. That's not going to make a major difference day to day, but it's nice to know where that extra weight is coming from. Now, if only Apple would add a bit more weight in order to bump up the battery life — that's a tradeoff we'd all be willing to make.

Thanks, Anonymous!

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