Every pair of Birkenstocks is made from the highest quality materials. EVA Upper / EVA EVA - Ethyl Vinyl Acetate is a non-toxic synthetic compound. Creates lightweight and flexible footwear that is shock absorbent. Also resistant to water, oil, and grease. It can shrink at high temperatures. Made from Ethylene-vinyl acetate, this footbed is lightweight and flexible and still offers contours and arch support while being completely waterproof.