Quality duvet covers should have internal corner ties that can be secured to the loops on your duvet insert. Some duvet covers may have four ties (one in each corner), while others may have up to eight (with extra ties at the middle of each side of the duvet cover as well). These should help prevent your duvet insert from bunching up inside its cover, but it's also recommended to regularly fluff your duvet when making the bed. Just raise it up and give it a few quick shakes to even things out. Duvet covers have buttons, a long zipper, or more fabric ties along one side as closures. Buttons or ties can feel a little tedious, but they tend to last longer than zippers do.