Thought I would post a confirmed figment and a great price for an air filter. As others have noted the factory filter is a BMW part number 13718635102. I found the Febi Bilstein brand at RM European on sale for $7.11 so I purchased two of them.
Most likely a resonance/expansion chamber to help tune impulses in the intake tract to help quiet it down or possibly eliminate unwanted turbulence of the airflow to help the air move more smoothly through the intake increasing efficiency slightly.
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