Design features include flat surfaces, plastic with a brushed aluminum look, angular shapes, and white accents in the interior. The Define Mini C Tempered Glass, with its tempered glass side panel, is a real eye-catcher and a highlight of any setup.

Like all cases in the Define series, the Mini C is soundproofed and visually dominated by the front panel in brushed aluminum look, which is only interrupted by a notch for the status LED at the top edge. The front panel is soundproofed on the inside. Behind it lies the first of three removable dust filters. There are ventilation slots on the sides that ensure optimal airflow within the case, further supported by the open design of the interior.

The I/O panel is integrated at the top in front of the lid. It houses, in addition to the obligatory headphone and microphone connections, two USB 3.0 ports, the power button, and the reset button. The lid is also soundproofed but can be removed to optimize airflow for the fans placed there. An included magnetic filter prevents dust from entering the case through the top. Another filter can be found at the bottom of the case, which can be pulled out from the front.