UpStart Battery 5-Pack Replacement V3900 Filter for Vicks Humidifier - Compatible Vicks WF2 Air Filter Replacement Vicks V3900 Humidifier Filter - Quantity, 5 Replaces Vicks WF2 Air Filter Traps Water Impurities & Dissolved Solids Before They Become Airborne For best results, change air filter at least once per season or more often depending on air quality and use. Essential for Allergy Sufferers. On Sale for a Limited Time!