Once you’ve filled your letters with blended curves, play with the curve layers, making them larger (Cmd/Ctrl + ]) or smaller (Cmd/Ctrl + [) until you’re happy with it. Create some white swirly lines inside the letter, especially around the white areas, using the Pen tool with a 0.1pt black line filled with white.
Once you’re happy with everything, it’s time to create those outside swirls. Unlock the Draft layer you created at the beginning. Choose all the lines, then select View > Guides > Make Guides (Cmd/Ctrl + 5).
Now we need to create a brush. We need a stroke that’s thin at the beginning and end: you can open the file material.ai from the files you opened at the start of the tutorial and copy each brush shape to your file – or create a line of your own, then click the Brush symbol and choose New Brush > New Art Brush > Proportional.
Now use the Pen tool to create a path that follows your curve guide. Then choose your brush, set it to a very fine stroke (0.1 to 0.25pt). Now trace over the swirls outside and inside the letters. Play with the opacity – setting it to 50% at the Normal blending mode, or setting the blending mode to Overlay and the opacity to 80% inside the letter.