Birkenstock Madrid Slide Sandal - Black Patent - Womens Synthetic Anatomically correct Synthetic footbed, crafted from Synthetic that is 100% renewable and sustainable, encourages foot health. Raised toe bar is designed to encourage the natural gripping motion of your feet, exercising your legs and aiding circulation. Neutral heel profile and deep heel cup keeps the natural padding of your foot where it belongs, under the heel, distributing your body weight more evenly.