How thin can a smartphone really get?
If you ask Samsung, it can go as low as 6.4mm – that’s how thick its upcoming Galaxy S25 Edge will be, making it the slimmest phone in the company’s 2025 lineup.
But that’s clearly not the limit as far as phones can go, and Tecno has proven it. The Chinese company’s new Spark Slim is an incredible 5.75mm, making it the world’s thinnest phone to date.
I’ve had the opportunity to try it at MWC 2025 in Barcelona, and it’s an incredibly impressive feat of engineering. It genuinely feels like you’re holding something from the future.
Anyron Copeman / Foundry
However, Tecno wants to emphasise that this is just a concept. The company has no plans to bring the Spark Slim to the market, even in its native China.
And it’s hardly surprising, as there are two key problems that I can see with this ultra-slim design.
The first is durability – the Spark Slim doesn’t have the sturdy feel you get from thicker and heavier phones, and it felt a little flimsy in my hand. If I accidentally sat on it or dropped it on the pavement, I’d be worried if it could survive.
Overheating is also a major concern. Tecno has supposedly managed to squeeze a 5200mAh battery into the Spark Slim, but that surely leaves no room for a proper cooling system.
In its current form, I’d be reluctant to use the phone for any demanding tasks, but even using it while charging would feel like a risk.
However, neither of those issues are a criticism of Tecno. Even in concept form, the company has shown that an ultra-slim device is possible, paving the way for a similar phone to be released in the future.
For its desire to push the boundaries, the Tecno Spark Slim is deserving of a place in Tech Advisor’s Best of MWC 2025 Awards.
