Apple has confirmed that its new foldable iPhone Duo is the thinnest iPhone the company has ever built, but only when the device is fully unfolded. According to Apple, the iPhone Duo measures 5.2mm thick in its open state, making it 0.4mm thinner than the 5.6mm iPhone Air.

The claim positions the iPhone Duo as a new benchmark for Apple's product lineup, though the final thickness fell short of some earlier expectations.

How Thin Is the iPhone Duo Really?

Rumors ahead of Apple's announcement suggested the foldable could measure as thin as 4.5mm when unfolded, putting it in the same range as Samsung's Galaxy Z Fold8. That didn't happen. At 5.2mm open, the iPhone Duo is only slightly thicker than the 5.1mm 13-inch iPad Pro, which remains Apple's thinnest device overall.

The picture changes significantly once the device is folded. In its closed state, the iPhone Duo measures 11.3mm thick, more than the 8.75mm thickness of both the iPhone 17 Pro Max and the iPhone 18 Pro Max. That gap reflects the mechanical reality of folding phones, which must accommodate a hinge and two stacked display layers when closed.

A Heavier Device With Dual Displays

Weight is another area where the iPhone Duo stands apart. At 254 grams, it is Apple's heaviest iPhone to date, five grams heavier than the 249-gram iPhone 18 Pro Max. The added weight comes alongside a new form factor: a 7.6-inch inner display for use when the device is open, and a 5.4-inch outer display for quick tasks when it's closed. Apple has given the phone a short, wide profile rather than the taller, narrower shape of its standard iPhones.

Hartley Charlton, reporting on Apple's announcement, noted that the two halves of the iPhone Duo connect into a single continuous frame, with both displays sharing the same aspect ratio. Apple said it designed the transition between the open and closed states to feel fluid, a detail aimed at making the switch between the two screens feel natural rather than like using two separate devices.

Why the Trade-Offs Matter

The iPhone Duo's dimensions illustrate the compromises inherent in foldable phone design. Achieving a thin profile when open typically means added bulk and weight when folded, since the hinge and dual-screen assembly must fit into a smaller footprint. Apple's numbers suggest it prioritized a sleek unfolded experience over minimizing the folded thickness, a decision that mirrors similar trade-offs other foldable makers have made.

For buyers comparing the iPhone Duo to the iPhone Air, the choice will likely come down to whether the larger inner display and dual-screen functionality outweigh the added thickness and weight when the phone is closed.

Availability

Apple says pre-orders for the iPhone Duo begin on October 16, ahead of an October 23 launch date.