cotton, these sponge sticks provide excellent absorption and filtration for your humidifier Keep your USB humidifier running smoothly with our 10-pack of replacement cotton sponge sticks Perfect for use in bedrooms, offices, and other small spaces where dry air can cause discomfort or health issues Ideal for anyone who uses a USB-powered personal humidifier to improve air and a more comfortable living or work space With four different sizes to choose from, you can easily find the right fit for your humidifier and enjoy clean, air wherever you go