What are Birkenstock EVAs? EVA (ethyl vinyl acetate) is a specialized rubber-like material. The Birkenstock EVA sole, (aka BirkoCork) is designed as a cushioned, lightweight midsole for arch support and comfort. Many Birkenstock EVA shoes are Vegan approved but they are flexible and waterproof while their color will not fade due to exposure to bleach or UV rays. As you can see, Birkenstock EVAs are not one particular type of shoe, but many -- Arizona, Milano, Roma, Mayari, Yara, and Gizeh.