Replacement Gas & Odor (GO) Smokestop particle and gas filters for the Blueair 200 and 303 series air purifiers. Includes 1 polypropylene pleated filter with 2 lbs. of activated coconut shell carbon impregnated with a 70/30 blend of Potassium Iodide (KI), Phosphoric acid (H3PO4), and Potassium Hydroxide (KOH) for gas, smoke and odor control. Filter can be vacuumed to prolong filter life and efficiency. Replace filter every 6 months.