Clarks Nature Three. This classic silhouette last is brought right up-to-date with the addition of state of the art Clarks Active Air underfoot cushioning. Clarks Active Air combines a pump hidden in the heel with state of the art materials and specialist construction. The result not only cushions feet, it also ventilates them by silently drawing fresh air in from outside.. The last word in comfort is complemented by a rich black leather, a rubber sole adds grip and durability.