https://www.pcgamer.com/deepcools-new-liquid-cooler-has-anti-leak-tech-to-avoid-drenching-your-pc/

All liquid CPU coolers should implement anti-leak technology, and to some extent, they do. DeepCool, however, spent three years developing a patented anti-leaking solution found in its newest Castle 240RGB V2 all-in-one liquid cooler that utilizes a pressure relief bag to avoid spillage.

This elastic bag sits inside the 240mm radiator with one side exposed to air and the other dipped in the coolant.