Soluble fiber is basically a gelatinous fiber that can bind with fats and move them through your body - essentially undigested. Insoluble fiber basically is fibrous plant material that goes out of your body essentially the same as it went in... not digested or broken down at all. They both have virtually no impact on blood sugar levels... the difference is in the form and in the case of soluble fiber it can actually bind with fats and move them out of the body without allowing them to be digested. This is an oversimplified explanation... but I am too lazy to go do a google search and pull up more specifics on the difference.