Papers for Watercolor Painting

Watercolor Paper
Watercolor paints should be used with paper made specifically for watermedia. Watercolor paper has a special surface sizing designed to accept the watery paints. Artists sometimes like to paint in sketchbooks or pads but paper made for drawing does not have the same kind of surface. Drawing paper also tends to wrinkle or curl severely when wet. Watercolor paper holds up better to paint. 

*  Hot Press has a very smooth surface. It is valued for accepting fine details. Paints can be lifted a little more easily from the surface. Watercolor paper also comes in a Roughsurface that allows a great degree of texture to show up quickly and easily.
*  Cold Press Fine watercolor paper has a fine bumpiness to its surface that many artists like for the variety of textures that they can create. Takes watercolor “washes” very wel.l Can be scraped or rubbed to add to the working techniques. 
*  Cold Press Rough allows a great degree of texture to show up quickly and easily. 

Weight  
* 90 pound paper is the thinnest or lightest. Likely to curl greatly when water is applied.  
*300 pound paper is fairly heavy. Less likely to curl but it also has a less flexible feel to it.
*140 pound is somewhere in the middle. It's a good compromise.

Note that thicker paper is also more expensive. Artists often try to save money by choosing the thinner paper but the difference is in the amount of curling or wrinkling.