Insoluble fiber does not dissolve in water. It does not get broken down by the bacteria in the large intestine. Since it passes essentially unchanged through the intestines, it produces little gas.

Insoluble fiber, also known as roughage helps Digestion by absorbing water in the intestine which results in smoother cleaning of the bowels. Cellulose, hemicellulose, and lignin are examples of insoluble fiber.