The Reese Duvet set is 100% cotton for sure. 
The fabric is soft, the color is bright, I really like it. The fabric is different on both sides. The top has a look of the gauze matierial which is really soft but really fragile to touch and washes. The underneath is a regular cotton. It is very nice to sleep on it, not warm at all for the pillow.
I like the product but i am sad to say it won’t last. Look at the pictures and see after just one wash how the gauze cotton is pulled. I am disappointed. I did wash it warm instead of cold as they recommend so it might be my fault but it is still very fragile.