As you may have read in the description, the bottle steriliser comes with a free HEPA filter. This “High-Efficiency Particulate Air” filter is vital to keeping your bottles as clean as possible and your baby as safe as possible. A HEPA filter comes into play during the drying process, helping keep mold, bacteria, dust, and pollen off your freshly drying bottles. Microscopic airborne particles risk affecting your little one’s health or allergies, so this bottle steriliser is here to help by providing extra protection while drying. Remember to replace the filter every 3 months for the best protection possible!