Rough Watercolor paper has a bumpy rough surface texture. The bumps and grooves help show the granulation in paints as well as creating high and low points on the surface texture, which can be used to your advantage when applying a dryer wash, allowing the white surface to show through. This type of paper is perfect for loose style and sgraffito techniques. 

Rough paper gains its texture, when It is pressed between sheets of textured felt during the drying process. Or handmade papers can be left to dry naturally, creating a less uniform, but interesting surface.