Video: How a Diesel Particulate Filter Works

Particulate-laden exhaust enters the filter. Because the cells of the filter are capped at the downstream end, exhaust cannot exit the cell directly. Instead, exhaust gas passes through the porous walls of the filter cells. In the process, particulate matter is deposited on the upstream side of the cell wall. Cleaned exhaust gas exits the filter.

Here are several videos that show the diesel particulate filter operation under different drive cycles.