Classic Double-row Design Our classic double-row roller derby skates are safer and more stable than straight-line roller skates, ideal for beginners and women or men who want to easily learn roller skating. Buy a pair, you can enjoy the fun of roller skating. Our high-quality PU leather wheels are perfect for indoor and outdoor use; therefore, you can stroll along the boardwalk at the beach, roller skating in the park, or wandering on the ice rink in a truly charming style . Flashing Four Wheels The principle of four flashing wheels - when the wheels rotate on the ground, they will generate friction and power, so the wheels can flash. It flashes only when the wheels slip. When the wheel is stationary, the wheel is transparent white (no battery or power supply required)