Pure cotton is 100%, but socks cannot be pure cotton. Spandex (PU) must be added during processing, otherwise it will not be elastic.

Spandex, translated as "Spandex", is a kind of elastic fiber, scientific name is polyurethane fiber (Polyurethane), abbreviation (PU). Called "spandex" in mainland China, it is highly elastic and can be stretched 6 to 7 times, but can quickly return to its original state as the tension disappears. Its molecular structure is chain-like, soft and extensible. Polyurethane, which enhances its properties by linking together hard segments. Elastic fibers are divided into two categories: one is polyester chain; the other is polyether chain. Polyester elastic fiber has strong resistance to oxidation and oil; polyether elastic fiber has good mildew resistance and detergent resistance.