Cold pressed paper as used for e.g. watercolours has a slightly rough surface. The peaks and troughs and slight randomness that it provides a good watercolour is amazing. In the valleys in the paper the pigment is being collected, and above that the white of the paper begins to appears translucently.
The opposite, i.e. Hard pressed paper is also used for watercolours, but almost only for those that require fine details such as architectural presentations. Hard pressed paper is used for most other paper art. The heat combined with pressure smooth the paper like an iron.
