Mindful of the environment, the industry increasingly turns to natural rubber outsoles that combine cushioning with flexibility. This renewable material can be used on its own or mixed with coconut husk fibers, cork and hemp, further reducing its environmental impact. Such alternative materials also help reduce the weight of a rubber outsole by as much as 40 percent, due to their lower densities.
Outsoles made of natural rubber can be found on everything from tailored pumps to novelty wedges reminiscent of the 1970s and from brands such as Terra Plana, Arche and El Naturalista. Although these bottoms are more costly to produce than their synthetic counterparts (such as EVA and polyurethane), due to increased difficulty handling the material, manufacturers are taking advantage of it nonetheless for the comfort and environmental advantages.
Rubber, a yellowish, elastic, amorphous material that comes from the latex or milky sap of various tropical plants, dates back to Mesoamerica (southern Mexico and Central America), 1600 B.C. But these days, the bulk of rubber is produced in Malaysia, Thailand and Indonesia, in climates near the equator, where rubber plants thrive.
Over the decades, the term rubber has come to refer to both natural and synthetic versions, the latter introduced in 1935 by German chemists. However, synthetic rubber is made with petroleum and is nonrenewable.
And while man-made rubber accounts for more than 75 percent of all rubber production, more companies are looking to make outsoles with recycled man-made rubber — especially from used tires — in combination with the natural material to help protect the environment.