Durable and waterproof material Lightweight EVA construction Fit Your toes and heel should not touch the rim of your sandals while standing in them. The extra room is needed to perform the natural rolling motion of the foot without restrictions - just as if you were barefoot. Birkenstocks are designed to be roomy. When you first try your sandals they might feel big. Most people are fine with a regular fitting, but if your foot moves side to side when you walk and adjusting the strap does not help, a narrow fitting may be more suitable. EVA Made from EVA Ethyl vinyl acetate, a non-toxic synthetic compound. Creates super lightweight and flexible footwear that is quite shock absorbent. Resists discoloration from exposure to bleach or UV rays. Also waterproof and resistant to acid, oil, and grease. Can shrink in heat over 170 Fahrenheit. Birkenstocks ever popular Madrid Sandal is now available with a lightweight yet durable EVA construction.