The Mediflow® Waterbase® was ranked best of all pillows tested in a clinical study at Johns Hopkins University. In fact, in all 5 categories tested subjects in the study ranked Mediflow best. Categories tested were, how long subjects took to attain sleep, how few times they awoke at night, how long it took to regain sleep after awakening and overall perception of sleep quality. The final category was neck pain and here subjects ranked Mediflow best in reducing the intensity of neck pain. Your head rests on a soft, plump layer of hypoallergenic polyester fiber which is supported by a thin waterbase at the bottom of the pillow. The waterbase responds to your head movement automatically as you sleep to maintain proper support for your neck. The Mediflow is the perfect pillow for all -- whether you're big or small or prefer soft or firm! Simply adjust the firmness of your pillow by adding the amount of water that provides the perfect level of support for you, soft, medium or firm. You can buy pillows for the entire family and they can all adjust them to their own perfect support level. Over 4 million people trust their sleep to Mediflow -- try it today and you will see why.