One of the elements that most affects your painting process and outcome is the paper that you choose to use.
Basically watercolor papers are available in three textures: smooth, known as hot-pressed; medium, known as cold-pressed, and rough. Paper is sold by the sheets or in pads and blocks.
Take a look at this. It is a piece of hot-pressed watercolor paper. There is almost no texture, so wet paint will cause puddles. First let me draw a thin line to show you how smooth the surface it is. This paper is very good for detailed artwork when the paint used is fairly dry. Now I apply a quite wet color here. Yes, it causes puddles.
This one is a cold-pressed paper. It has a distinct texture, although not enough texture to interfere with the flowing of the brushstrokes. Cold-pressed is the best all-purpose paper, we will use cold-pressed for all our exercises and demonstrations.
This is a rough paper. Rough paper has a pronounced texture, enabling the paint to settle in the raised grain to create broken-color and textured effects. It is not suitable for fine detail work. And now you can see how a rough watercolor paper respond to brush and paint.
Watercolor papers also vary from very thin to very thick. Although the weight is expressed as pounds, it actually refers to the weight of 500 sheets. Paper can be as light as 60 pounds or as heavy as 300 pounds. The thicker and heavier the paper is, the more it costs.
Keep in mind that the watercolor papers made by different manufacturers can also be quite different. For example, a cold-pressed 140-pound paper made by one manufacturer can be distinctly different from a cold-pressed 140-pound paper made by anther manufacturer. Their water-absorbency can be different as well as how the paper responds to the paint and brushes. This is often quite frustrating for artists who switch from one brand of paper to another. To find out what paper is most suitable for your own painting style and expression, you would need to spend time to experiment in order to understand the personalities of the different papers.