Birkenstock Adjustable Recovery Clog - Boston EVA. Features: Lightweight clog style, Flexible design on a contoured footbed. Content: EVA Upper, Lining, and outsole. Measurements: Sole Thickness- 1/3". Fit: True to size. Birkenstock ultra-lightweight style. The Boston EVA is made from water-friendly material, giving you a flexible design built on the contoured footbed you love most. The perfect pair for pre-workout, post-practice and all the rest days in between.