While not all brands have all the ingredients clearly listed on the box, you should be able to find that info on their websites. In an email with BuzzFeed Life, a representative from Procter & Gamble (makers of Tampax tampons) confirmed that its tampons are made of cotton and rayon. They have a thin fabric over wrap made of polyethylene and polypropylene, which are materials used in many hygiene products and surgical products (like other tampons, pads, and sutures).
"Tampons are regulated by the FDA as medical devices and are therefore required to meet the strict safety expectations of the FDA," a Procter & Gamble representative told us via email. "Our products and the materials they are made of are thoroughly evaluated for safety before we put them into the marketplace."
The website for O.B. tampons says O.B.'s tampons are made of rayon with a polyester string. They also have a polyethylene/polypropylene film. Kotex tampons are made from cotton and rayon, according to the company's website.