Woven polyester fabrics are developed to a very high standard. Polyester is the most used sailcloth, known as Dacron, Tetoron, Terylene, Trevira and Diolen too.
Technically, Taffetas are all types of fine, light woven fabric (for example silk). Taffeta for sail production are tight woven polyester as layer on laminates for better resistance against UV, tear, flex and chafe.
Nylon can be woven very tight, fabric is light and strong.