For a time, it was unclear whether the flip or fold form factor was the future of folding smartphones, but for now at least, it seems clear that the book-style fold is the winner.

It’s what we saw from Samsung’s 8th-generation folding phone, it’s what we’re expecting from the iPhone Ultra, and leaked images of Xiaomi’s 18 Fold also follow the trend …

There are two form factors for folding smartphones, colloquially known as the flip and the fold.

The flip design essentially has a conventional smartphone fold in half to a device which is thicker but half the height. This provides a standard-sized screen in a more pocketable format. The Motorola Razr is one example of this, and it echoes a design the same company first popularized way back in 2004.

The fold format, now increasingly referred to as a “book” design for obvious reasons, takes a device with a squarer shape and then unfolds into the equivalent of a small tablet like the iPad mini. This is the design Apple is set to unveil next month.

Samsung has popularised this with its Galaxy Z Fold series, with the 8th-gen model released just last month.

Xiaomi is now set to join the party with its 18 Fold, whose camera island bears more than a passing resemblance to the expected look of the iPhone Ultra. Weibo user Peter shared two photos (above) of what he suspects to be an engineering prototype rather than the actual production model.

Our sister site 9to5Google notes that the dark cherry color appears to have been based on rumors of one of the iPhone 18 Pro colors.

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Image: 9to5Mac/Peter/Annie Spratt

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