Optional rain sock/pre-filter; for adverse weather conditions. Similar to the K&N pre-chargers. Silicone treated; polyester filter wrap. contain uniform micron sized openings that allow high air flow. Yet; due to the Drychargers silicone treated polyester wrap; the amount of water that reaches the air filter or flame arrestor is limited. - Wraps your air filter with an additional pre-filter - Extends service interval of your K&N filter - Durable silicone treated polyester material with stitched elastic openings - Water repellent treatment typically lasts 1 to 2 years - Base inside diameter: 6.25" (159mm) - Top inside diameter: 5.50" (140mm) - Height: 2.125" (54mm)