NWT Pottery Barn Kids Vivienne Duvet and Sham. 2 Available A print that’s pretty fabulous, this butterfly duvet cover strikes an entirely new note using both soft and bold elements. Pure cotton percale. Duvet cover and sham reverse to self. Duvet cover has a hidden button closure; sham has an envelope closure. Made of 100% cotton percale with 4% organic cotton fibers. A percale weave is noticeably denser and wears well over time. Duvet cover is finished with interior corner ties and a button closure to keep the duvet in place.