What is the difference between regular buckwheat hulls and Sobakawa hulls?

They use this to fill bed pillows in Japan. They have been advertised on T.V., but I don't know the difference between the regular hulls and the Sobakawa. Which is better and why? "They" say not to buy the pillows that are made in the U.S., but the ones only from Japan. I would like to buy some, but, even though I looked it up on the internet, I still don't know which is best or why. Can anyone help?