The standard bento box carbon filter is too restrictive. When you assemble it the fan actually speeds up and little-to-no flow goes through the device. This is because the fan blades are stalled. The carbon bits in the standard carbon filter box they cover the holes and the fans pull down…which just futher holds the charcoal bits down. My design allows air to flow freely between carbon containing sections, with some of it passing through the carbon. It lets the air flow.