Simple textured brush that looks like something between a creamy pencil and a marker. Flexible, used mostly for lineart or sketching.
This is the main brush I use for everything I make. Its tip looks like a silkworm, therefore the name, but it gives a kind of pencil-ish textured effect in drawing.

This drawing uses the silk worm marker and CSP's default gpen alone. The brushes opacity and strength of texture harden on pen pressure but the brush size stays mostly consistent. Keep in mind the opacity and texture when using this for coloring as the coverage may, in the end, make the colors a little inaccurate.