The neoprene replacement foot bags fit on every NUNUI monofin and kann be replaced easily. The NUNUI monofin itself is not supplied, beacuse it is a spare part. The foot bags cover the shoe sizes EU 39 - 43. It is made of an durable cover made of neoprene material, which holds your feet securely in the pocket with your monofin. Since the water pull on the footbag can be quite big for fast fast and powerful swimming especially for adults, it is absolutley necessary to replace defective foot bags. The neoprene foot bag is an object of wear and tear. for this reason, this can be easily replaced.