Birkenstock Classic Boston Regular Fit Smooth Leather BlackThe Birkenstock Boston clog has an adjustable strap ensuring an individual fit. The highest quality leather is used between 2. 8 and 3mm thick. The leather footbed makes them comfortable to wear and creates a pleasant environment for the entire foot. These clogs are suitable for a range of occasions whether indoors or out. With a simple; adjustable design and contoured cork footbed that forms to the shape of your foot; the Boston is a proven classic.