Great to have on hand as an extra or a replacement for an old filter, this set of two yellow Bobble replacement filters will fit on any Bobble water bottle. With an activated carbon filter with a slight electro-positive charge, they attract chemicals and impurities. As the water passes over the positively charged carbon surface, the negative ions of the contaminants are drawn to the surface of the carbon granules. Carbon filters require very little maintenance, and are perhaps the most powerful chemical absorbents known. Each filter is good for two months or 40 gallons of water, which is approximately 300 refills. Made in the USA, they are BPA free and FDA approved.