Polyester is a kind of chemical fiber, including polyester, nylon, spandex and acrylic fiber. Fiber also includes cotton, hemp, wool, silk and so on. Are all concepts in the same scope.
Ultra-fine denier is the concept to explain the thickness of fiber. Among them, denier is a unit, which means how many grams of fiber is 9000 meters long. Ultra-fine denier means that this fiber is very fine. As for how fine it is, there is no clear standard in the national standard and the industry standard of textile industry. Usually refers to fibers with fineness of 0.5~5dtex.
The relationship between superfine denier and polyester can be understood in this way. Polyester varieties include superfine denier, fine denier and coarse denier, while nylon has superfine denier, coarse denier and conventional denier. I hope I can help you.