Flee.official - Posts | Facebook- face mask dust mask สเปรย์ป้องกันไวรัสแบบครอบหู ,Measure dust before covering and after covering over time. Value decreases to almost 0 = pass , if the value doesn't decrease or less = time to change . Importantly, when our kids wear mask, they need to be fit, not loose or fall down to prevent infections and dust effectively. 😄 . For mothers who want to find a new mask for their children.