Soba means buckwheat in Japanese and soba noodles are made from a mixture of buckwheat and wheat flour or sometimes from pure buckwheat flour. Soba noodles can be eaten hot or cold. To get the most out of the unique buckwheat flavor, look for noodles that have a high buckwheat content. However, wheat helps keep the noodle together, so there's a balancing act. I’ve been boiling 100% buckwheat soba when I'm serving them chilled and I haven't had any issues, but you do need to pay attention and not overcook them. I order Mitoku soba noodles from naturalimport.com, which stocks different buckwheat contents including organic options.
All of the above applies to dried soba noodles. I have yet to try making fresh soba noodles. It's probably a lot of work and very tasty.