Ultra-thin 120mm CPU fans are a specialized type of cooling solution that caters to specific computer case designs and cooling requirements. These fans are extremely thin, usually with a thickness of less than 25mm, which is significantly thinner than standard 120mm fans that can be around 25-30mm or more. The ultra-thin design makes them ideal for use in slim computer cases, such as those used in all-in-one PCs or some ultrabook docking stations. In these applications, space is severely limited, and a traditional fan would not fit.

Despite their thinness, ultra-thin 120mm CPU fans are engineered to provide a reasonable level of cooling. They achieve this through optimized blade designs that focus on maximizing airflow efficiency rather than sheer volume. The blades are often shaped in a way that allows them to cut through the air more effectively, even with a reduced overall thickness. Additionally, the fan motors are designed to be compact and efficient, minimizing power consumption while still providing sufficient rotational force. These fans may also use advanced bearing technologies, such as fluid dynamic bearings, which offer a good balance between quiet operation and durability. However, it's important to note that due to their thin design, ultra-thin 120mm CPU fans may not have the same cooling performance as standard 120mm fans. They are best used in systems where the CPU heat output is relatively low or in combination with other cooling methods, such as heat pipes or passive cooling elements, to achieve an acceptable level of thermal management.