Let's talk surfaces. Mixed Media papers typically have a medium/vellum drawing surface with a slight amount of tooth (texture) that works well with mediums like graphite, marker, pen & ink, and colored pencil. Traditional watercolor paper typically has more tooth, which does not allow for finer details or creating depth of tone when using dry mediums. The most common watercolor paper surface is cold press. Cold press paper has a good amount of texture or 'peaks and valleys' on the surface. The paper fibers are more loosely compressed than a mixed media paper. This allows the watercolor to penetrate deeper into the paper. Watercolor papers are also available in hot press. This term refers to the end of the paper making process, when the paper passes through large rollers that are tightly compressed. The added pressure of the hot press process creates a smoother surface. A hot press paper will more resemble a mixed media surface than a cold press paper.
Wet Media: Watercolor papers are sized to handle wet media applications. Sizing refers to the additives and papermaking process that makes the sheets less porous while still absorbent. Without sizing, the paper would buckle. Sizing also allows for a more uniform wash and the ability to lift color off the paper without the surface pilling.
Dry Media: Many artists like to incorporate dry media into their watercolor pieces, for which watercolor paper is not ideal. The peaks and valleys in a cold press paper do not allow for fine details when drawing with graphite. Mixed Media paper allows an artist to work in watercolor and add detail in other mediums or start by adding detail with ink or marker and then add watercolor.
Conclusion: Mixed Media is a hybrid between a drawing and a watercolor paper (surface of a drawing sheet + sizing of a watercolor sheet). This is the ideal surface to use for urban sketching or whenever you're using a variety of materials. If you are only working in watercolor and want a paper that will react specifically to watercolor techniques, then we recommend choosing the highest quality hard or cold pressed watercolor paper for your needs.