Twin Air Standard Air Filter — Yamaha YZ 400 (1977-1978)

Twin Air's Standard Air Filter is the dual-stage foam filter that's been the benchmark in dirt-bike air filtration for decades. Two fused layers of open-pore foam — coarse outer, fine inner — trap airborne dust, grime, and sand while keeping airflow high. Assembled by hand and inspected for fit, with model-specific molds for 1500+ motorcycles dating back to 1965.

• Dual-stage open-cell foam — outer catches grit, inner traps fine particles
• Hand-assembled and inspected, with a greaseless sealing ring
• Washable and reusable — 30+ cleaning cycles is typical
• Model-specific fit — no universal sizes
• Drops into the OEM airbox