I made lightweight blankets for my girls because it has been pretty warm here and their comforters are just too heavy. When I covered them with a lightweight fleece at night, I realized it was exactly the same size as half of a twin sheet. I decided to sew up the sheet and make a duvet cover so I could easily remove the fleece.
I sewed each duvet cover out of one flat sheet and one fleece blanket. Here you can see the fleece blanket laid over the folded twin sheet. The blankets were approximately 50 x 60". The twin sheets are from Target and were larger than other sets we owned so double check the size.
It all took less than an hour. It was very simple to sew, I did not even use pins. I just started at an unfolded corner and sewed to the folded edge. This way I ensured the material would not move around too much. I left about 10" open on the bottom edge so I could remove the blanket for washing.
Here is the finished product on a toddler bed (left) and on a twin bed (right).
