Prepare all your fillings: julienne carrots and cucumber, chop fresh herbs, and soak the bean thread noodles until tender, then drain well.
Fill a large shallow dish with warm water, about 40°C / 104°F. Submerge one rice paper at a time for 10-15 seconds until it becomes soft and pliable, then gently lift it out and lay it flat on your damp towel.
Place the softened rice paper on your workspace, keeping it moist with the damp towel nearby. Spread a small handful of the vegetable mixture about one-third from the bottom of the wrapper, leaving a 2 cm border on each side.
Add a few strands of soaked noodles and optional protein slices on top of the vegetables, then fold the sides inward over the filling.
Gently roll the rice paper upward from the bottom, keeping the fillings snug but not squished, until the seam is sealed and the roll is firm.
Transfer the completed spring roll to a serving platter, cover with a damp towel, and repeat the process with remaining rice papers and fillings.
Let the assembled rolls rest for about 5 minutes to allow the flavors to meld and the rice paper to settle.
Serve the spring rolls with your favorite dipping sauce on the side, and enjoy immediately for the best crunch and freshness.