Use 90-lb. watercolor paper if you are practicing watercolor painting, creating quick watercolor sketches, or are on a budget. Dampen 90-lb. watercolor paper with water, attach it to a flat board with tape, and allow it to dry completely before painting on it to ensure that this very light paper will not buckle and crease when you use it.
Use 140-lb. watercolor paper for paintings that require more paint and water. Dampen 140-lb. watercolor paper with water, attach it to a flat board with tape, and allow it to dry completely before use, to ensure that it doesn't buckle or crease when you paint on it.
Use 300-lb. paper for serious watercolor paintings that use a lot of paint and water. Do not stretch 300-lb. watercolor paper.