Normally strip or jacquard designs are used for duvet cover. Both of 100% Cotton 300TC Strip and 250TC Strip are the most popular. By the way, it’s up to your need because plain can also use for duvet cover.
Yarn Count: 300TC Jacquard, 300TC Strip, 250TC Strip
King Duvet Cover: 100”x90”x15”
Queen Duvet Cover: 90”x90”x15”
Twin Duvet Cover: 70”x90”x15”