Samsung is reportedly setting an aggressive thinness target for the Galaxy Z Fold9, with a new leak claiming the next-generation foldable could measure just 7.9mm when folded and 3.9mm when unfolded. If accurate, it would be the slimmest book-style foldable Samsung has ever attempted, and it would widen the design gap with Apple’s far chunkier iPhone Duo.
The claim comes from leaker @kro_roe, who posted the figures on X on 1 October. According to the report, picked up by mobile press on 5 October, Samsung has set the slim profile as an internal engineering target for the Fold9 as it looks to strengthen its lead in the increasingly competitive foldable market. Samsung has not announced the Galaxy Z Fold9 and has not confirmed any dimensions, so these numbers should be treated as development goals rather than final specifications.
What the Galaxy Z Fold9 leak actually claims
The headline numbers are striking. A 7.9mm folded thickness would make the Galaxy Z Fold9 noticeably slimmer than the current Galaxy Z Fold8, which is said to measure around 9.7mm when closed. Unfolded, the claimed 3.9mm profile would undercut the Fold8’s reported 4.5mm. In a device category where every fraction of a millimetre affects how the phone feels in a pocket or a jacket, a reduction of nearly 2mm folded would be genuinely noticeable in daily use.
It is worth stressing how early this information is. The figures describe a concept-stage target, not a finished prototype, and Samsung’s engineers still have to prove the design can survive real-world durability testing. Foldables live or die on their hinges and flexible displays, and chasing extreme thinness can force compromises on battery capacity, camera hardware and structural strength. Until Samsung shows hardware, the 7.9mm figure is best read as a statement of intent.
Galaxy Z Fold9 vs iPhone Duo: the thickness gap
The comparison that matters most is with Apple’s first foldable. The iPhone Duo, which is heading for pre-orders, is reported to measure 11.3mm folded and 5.2mm unfolded, and it weighs around 254g. Against those numbers, a 7.9mm Fold9 would be roughly 30 percent thinner when closed, a difference anyone would feel immediately.
- Galaxy Z Fold9 (leaked target): 7.9mm folded, 3.9mm unfolded
- Galaxy Z Fold8 (reported): 9.7mm folded, 4.5mm unfolded, 201g
- Galaxy Z Fold8 Ultra (reported): 8.9mm folded, 4.1mm unfolded, 215g
- iPhone Duo (reported): 11.3mm folded, 5.2mm unfolded, 254g
Weight tells a similar story. The current Galaxy Z Fold8 is said to weigh just 201g, lighter than many conventional flagship phones, while the iPhone Duo is reportedly a hefty 254g. Complaints about the Duo’s bulk have already surfaced among early observers, and Samsung clearly sees an opening. If you want the full picture on Apple’s foldable pricing and UK availability, read our guide to iPhone Duo pre-orders and what the £1,999 foldable means for UK buyers.
Why thinness matters more on a foldable
On a normal smartphone, shaving a millimetre is a nice-to-have. On a foldable, it changes the whole experience. A book-style foldable is essentially two phone halves stacked together, so any excess thickness is doubled when the device is closed. That is why early foldables felt like carrying a small wallet, and why each generation’s slimming-down has mattered so much to buyers.
There is also a psychological factor. Foldables are premium devices with premium prices, often well above £1,500 in the UK. Buyers paying that much expect the phone to feel like the future, not like a prototype. A Fold9 that closes to under 8mm would feel closer to a regular flagship in the hand, removing one of the last practical objections to switching to a folding phone.
The engineering challenge is real, though. Samsung will need a redesigned hinge, a thinner flexible display stack and clever battery packaging to hit these targets without making the phone fragile. The company’s years of foldable experience give it a head start over Apple, whose first attempt at a folding iPhone has landed on the chunky side, but ambition on paper still has to survive the factory floor.
Should UK buyers wait for the Galaxy Z Fold9?
For most people, the honest answer is probably not yet. The Galaxy Z Fold9 is not expected until next year, and leaks this early routinely shift before launch. If you need a foldable now, the current Galaxy Z Fold8 remains the benchmark for thin and light book-style phones, and its price will likely soften as the Fold9 approaches.
But the leak is still significant. It signals where Samsung thinks the foldable battle will be won: not on cameras or chips, but on industrial design. Apple may have finally entered the foldable arena, yet on thickness and weight Samsung is playing a different game. If the Fold9 lands anywhere near 7.9mm folded, the iPhone Duo could look outdated within months of its release. For UK buyers weighing a £1,999 Duo against Samsung’s next move, patience might be the smartest upgrade of all.
