Birkenstock Birko Natural Insole (Unisex)BirkoNatural this footbed is wonderful for your feet and is natural, too. The footbed contains natural and renewable resources (e. g. cork, leather, jute). The foot friendly, anatomically shaped footbed naturally cushions and supports the foot. BirkoNatural puts a spring in your every step and reduces the strain on the spine, knees, and hips. Its length means this insole will fit into most types of footwear. Vegetable tanned leather lining Cork latex