Sōmen and Nagashi Sōmen

Sōmen (素麺^?) are very thin—less than 1.3 mm in diameter—white Japanese noodles made of wheat flour.

The noodles' diameter is the chief distinction between sōmen and the thicker wheat noodles hiyamugi and Japanese wheat noodles udon.

Sōmen are usually served cold with a light flavored dipping sauce or tsuyu.
In the summer, sōmen chilled with ice is a popular meal to help stay cool.

Sōmen served in hot soup is usually called "nyumen" and eaten in the winter, much like soba or udon are.

Some restaurants offer nagashi-sōmen (流しそうめん flowing noodles) in the summer. The noodles are placed in a long flume of bamboo across the length of the restaurant. The flume carries clear, ice-cold water.

As the sōmen pass by, diners pluck them out with their chopsticks and dip them in tsuyu. Catching the noodles requires a fair amount of dexterity, but the noodles that are not caught by the time they get to the end usually are not eaten, so diners are pressured to catch as much as they can.

A few luxurious establishments put their sōmen in real streams so that diners can enjoy their meal in a beautiful garden setting.

Machines have been designed to simulate this experience at home.