K&N replacement High-Flow drop-in air filter for BMW 135i/335i/335i xDrive and X1 35i (2011–2014) is constructed from layered, oiled cotton media to improve airflow and capture contaminants, and is designed to increase horsepower. The washable, reusable filter installs in the factory air box and is backed by K&N's No-Hassle Lifetime Limited Warranty for long-term service.
K&N 10-12 BMW 135i/335i/335i XDrive/X1 35i 3.0L L6 (E90) Replacement Air Filter