An outerwear pre-filter is a washable, reusable protective layer, typically made of durable, silicone-impregnated polyester mesh, that fits over a primary air filter to capture large debris like sand and dirt, thus protecting the engine, extending the life of the main filter and maintaining airflow and horsepower. Unlike oiled filters, it's a "run dry" product that repels water and prevents dirt from sticking to the filter material, which would restrict airflow and cause horsepower loss.
