Pastel is a dry media, softer than chalk, but like chalk it has infinite brush loading. Applied with the Pastel tool , its dry pigment tends to penetrate the canvas texture proportional to the pressure with which you apply it. Pastel pigments have a fixed viscosity that is slightly less than chalk, meaning the strokes you apply leave some volume on the canvas as they break from the pigment stick. Pastels do not have a bristle component to the stroke, instead presenting a flat or angled surface of the stick. The stroke edges fall off and break up based on the texture of the canvas.
Pastel is slightly shiny, interacts with itself by smearing slightly, and dirtying the tool head slightly when applied with light pressure. It loads the canvas more than chalk, breaking up more when applied, and this gives the appearance of volume to the surface.