Made of TPE, a high performance thermoplastic elastomer that stretches easily, Active SEAL maintains a waterproof seal.
Yoga mats made from thermoplastic elastomers, or TPE, are considered to be people-friendly as long as they do not contain PVC or latex.
Technically, TPE isn't a rubber at all, and doesn't contain any rubber bi-products, but it's often described to consumers as synthetic rubber for ease of understanding the product and to reduce any confusion with PVC.
However, you'll have to contact its customer service department to determine if the mats are natural or TPE, as the descriptions don't clarify.
Barefoot Yoga Company carries both natural rubber/jute combination mats and TPE mats.