Made from wheat flour kneaded with salt and water, somen noodles are the thinnest Japanese noodle Ð just under 1.3 millimeters thick when uncooked. When they are thicker than this, they are known as hiyamugi. It is thought that somen acquire a better texture when dried and allowed to mature for up to three years. Somen and hiyamugi are commonly eaten cold, especially in summer, together with a dipping sauce and garnishes such as grated ginger and spring onion. They are also eaten hot in broth (nyumen).