Birkenstock Kid's Derry Rain Boot (Toddler/Little Kid)Size Chart Ready to get outside, regardless of the weather: the BIRKENSTOCK Derry offers optimum protection for feet because the comfortable and supporting footbed remains dry, even during pouring rain. The upper is made from extremely light and flexible EVA. This high quality, odor neutral synthetic material which has been tested for harmful substances is shock absorbent, waterproof, and skin friendly. Anatomically shaped BIRKENSTOCK footbed made