On Friday, we tore down Apple’s two newest iPhones and found something new lurking (quite literally) just below the surface. When we opened up the 6s, we discovered some mystery adhesive around a display that’s already secured with screws. Weird. It’s not as if past iPhone displays were in danger of falling out of the phone. In fact, they can be pretty tough to remove (which is why grunt-saving tools like the iSclack have a favored place in our tool bag).

iPhone 6s, now with 100% more of that white band you can see under the display. But what was it for?

So if the iPhone display didn’t need adhesive, what was Apple up to?

We had our suspicions, based in part on Apple patent filings in one particular area: waterproofing. Apple has been investigating a waterproof (or, more accurately, liquid proof) iPhone for at least the last several years. If that strip of sticky goop on the 6s wasn’t put there to hold the display in, then maybe—just maybe—it was designed to keep liquids out. Like a gasket!

Of course, that was only a theory. But over the weekend some brave Apple fans introduced their new iPhones to a life aquatic. The phones didn’t always emerge unscathed, but the overall trend is clear: the 6s and 6s Plus are dramatically less prone to liquid damage than their predecessors. (They aren’t, of course, completely waterproof—so don’t jump into a pool with them or anything.)

So, what changed? After disassembling a couple of new iPhones in the name of science, here’s what we found.

Plucking away the perimeter gasket: Oh, Apple, only you would think to use color-coordinated gasket strips—white or black, depending on the color of the display.

First, Apple takes this gasket business pretty seriously: they didn’t just run a strip of glue around the existing display like they were caulking a bathtub. Instead, it appears the iPhone’s frame has been subtly reworked to accommodate the new gasket. We noted a slight, but measurable, increase in the width of the lip running along the perimeter of the frame—it’s about 0.3 mm wider than on the iPhone 6, making it just wide enough for that little gasket to land on. One-third of a millimeter may not seem like much, but given how tight the iPhone’s tolerances are nowadays, the change is big enough to see with the naked eye. And it’s almost certainly enough of a change that other components had to be subtly tweaked to match. Make no mistake, Apple gave this careful thought.

The old iPhone 6 had a thin lip along the edge of the frame for seating the display. Here we show the lip and frame together, measuring roughly 1.89 mm.

But the same measurement on the new iPhone 6s reads 2.21 mm—enough room to seat that new gasket.

The logic board brought a bigger surprise. Every cable connector on the board—from the battery and display, to the Lightning port and buttons—is surrounded by what appears to be a tiny silicone seal. Those little connectors are the most vulnerable bits of the device—quick to short out and corrode during unplanned aquatic excursions. Apple filed a patent for waterproof silicone seals on board-to-board connectors just this past March. It appears this is one patent they’ve rapidly put into production. (The jury is still out on the second piece of that patent, a hydrophobic conformal coating for printed circuit boards. We’ll update this post if our tests can confirm whether it’s there.)

Tiny seals—those black, foam-looking hedges you can see around the gold connectors—surround all the logic board cable connectors.

Other parts of the iPhone 6s did not change dramatically in terms of waterproofiness. As we noted in our initial teardown, the power and volume buttons underwent a minor redesign, but they haven’t yet adopted the more radical waterproof profile seen in Apple patent filings. Perhaps Apple will save that particular innovation for the iPhone 7 (rumors have pegged the iPhone 7 as fully “waterproof,” as opposed to just water resistant.)

Finer 6s speaker mesh, top (iPhone 6 mesh on bottom).

No obvious signs of waterproofing in the speaker or headphone jack, either. The speaker sports a slightly finer mesh weave than that of the iPhone 6, but it doesn’t appear to repel water any better—in our tests, both speakers seemed to gulp down liquids at about the same rate. The SIM tray has been slightly altered as well, but it doesn’t look to be any more waterproof.

Those speakers still drink up their fill of water—6s on left, 6 on right.

So, there are still places for water to get into the case. Maybe that strip of goo around the display isn’t for waterproofing after all, but has some other nefarious purpose; 3D Touch is a new technology, so it’s hard to say. Nevertheless, we think this is an exciting step forward for the iPhone and its fans. You can repair your iPhone 6s just as easily as its predecessor—and while it’s not necessarily “waterproof,” the added water resistance means you’re less likely to have to repair it in the first place.

We call that a win. Here’s a video summary of our investigation:

We’ve updated the existing teardown with our newest findings, too. So wander on over to the teardown for more pictures and analysis on the entire device.

Jeff is a teardown engineer with iFixit.

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