Apple's tech specs put the iPhone Duo at IP68 under IEC 60529, tested to a maximum depth of six meters for up to 30 minutes. The iPhone 18 Pro and Pro Max carry the identical rating and the identical depth, so the folding phone is not rated lower for folding. Reading the spec pages across the September lineup, The Mac Observer found no listing for salt water, chlorinated pools, hot water or high-pressure jets. Six meters is a ceiling in a lab.
Apple built the Duo around a Grade 5 titanium enclosure, a precision hinge of more than 100 components, a 3D-printed hinge cover, internal support ribs, ceramic fiber inserts around the antenna sections and Ceramic Shield 2 over the outer display. Andrew O'Hara handled the phone at Apple's event and found the dip along the crease basically imperceptible, with the center of the inner panel holding firm when he pushed on it. By his account the Galaxy Z Fold 8 has no equivalent rating.