Birkenstock Boston Essentials EVA Clogs. The Birkenstock Boston is a veritable classic that can easily be worn all year round. The Boston has a legendary status thanks to its sophisticated, individual design. Shown in EVA, a synthetic waterproof and lightweight material. Super lightweight - great for after the gym or the beach. Anatomically shaped Birkenstock footbed made from EVA. Upper/lining/sole: a single piece of EVA. Waterproof, washable, ultra lightweight. Imported.