High-quality, heavyweight paper. Taller, stronger sides to help avoid overflow of grounds. Paper stock produced using an elemental chlorine-free (ECF) bleaching method. Allows for proper flow of water to produce consistent flavor profiles. Manufactured from high quality, heavy weight paper, so the water flows properly through coffee/tea. Uniquely designed for strength so the sides are taller and you don't end up with overflow and grounds in your coffee. Produced using an elemental chlorine-free (ECF) bleaching method.