aFe Power 31-10161 Magnum FLOW Pro DRY S Air Filter

The aFe 31-10161 is a washable dry synthetic non-woven replacement filter for Subaru EJ-platform WRX and STI applications. The Amazon listing covers 2008–2014; community reviews confirm fit on 2019 WRX Limited and WRX variants as well — including a reviewer who documented that K&N and Spectre did not fit the same air box. The oil-free Pro DRY S media eliminates the filter oil migration concern that affects oiled cotton gauze filters on some MAF-equipped vehicles; reviewers specifically note this as a key differentiator. The manufacturer claims 99.2% filtration efficiency, but no test standard (ISO 5011 or SAE J726) is cited in any available documentation — that figure is an unverified manufacturer claim. "Dramatic Airflow Increases" claims are not backed by independent dyno data; one long-term reviewer explicitly states the reusability benefit is real regardless of whether a power gain materializes.

The right pick for a Subaru EJ-platform WRX or STI owner who wants a long-service washable filter without the oiling step — particularly relevant for the 2019 WRX Limited, where this is the only confirmed drop-in fit after K&N and Spectre reportedly fail to seat. 2015–2021 WRX owners with FA20DIT engines: that platform uses a different air box geometry; fitment for those applications is unconfirmed — check aFe's application guide for your specific year and trim before ordering.

Passive replacement component — no chemical exposure pathway during installation or removal; no SDS applies. Environment score of 6.9 reflects the washable reusable lifecycle: a single filter can serve the vehicle for 100,000+ miles, eliminating multiple disposable replacement cycles, and the oil-free construction means no cleaning oil waste stream at service intervals. If an aFe cleaning kit is used to service this filter, review that product's own page for any PPE guidance.