Jason Jason why is it so big?
My goal with all of this was to make the computer as quiet and clean as possible. Mixing these two traits poses a challenge (while still keeping the airflow up/heat down) because they compete. To keep the case clean, you need a filter. But filters tend to restrict airflow, and make your fans have to speed up (ie. get noisier) to provide the same amount of cooling. Worst of all, any "normal" filters you buy for computers are terribly ineffectual when it comes to trapping dust. All they're really good for is trapping larger particles like cat hair. They have larger pores so as not to restrict airflow as much-- which they still fail at while only capturing half of the dust (I've tried numerous brands to compare; some decrease dust and airflow a lot, some decrease both very little, but it's always proportional).
The reason for this is their small surface area. The more surface area you have, the greater volume of air that can pass through travelling at the same speed. My filter is 50cm x 63cm. The filter's surface area is approximately doubled by the folds in it. This provides enough surface area that my case fans can pull as much air as they need at their normal RPMs without the need for a more porous (read: ineffective) filter.
Another major design consideration was to make sure the air pressure inside my case stayed greater than outside (most computer cases are the opposite

). This is to prevent dust entering my computer through cracks and holes in the case, as air will always be flowing out, not in. To accomplish this, I have 3 intake fans (2 120mm, and 1 80mm; two of the fans are hidden in the pictures; there is one on the front and one on the bottom of the case) and I have 1 exhaust fan (the one in my power supply) and 2 open vents. I tested all vents and holes on my case for sufficient outward airflow using a small square of paper attached to a thread. Higher air pressure inside the case may have some small cooling bonus as well since higher density theoretically means higher thermal transfer. Just an idea, but it's doubtful that it's of much significance in this case.
In summation: Huge filter = zero dust and zero reduction in performance.