Duvet inserts are comforters that feature duvet tabs on each corner to use with a duvet cover. While you can use a duvet cover with any comforter, it is a lot easier to use one with duvet tabs, as this enables your comforter to move with the duvet cover over time. If you never plan to use a duvet cover, you can skip the duvet inserts and shop for your next favorite comforter.
For more information on caring for your duvet insert, check out how to properly wash your comforters or how hotels keep their bedding so white.