From a conversation in a FB group.

There are 2 different types of fiber -- soluble and insoluble. Both are important for health, digestion, and preventing diseases.
Soluble fiber attracts water and turns to gel during digestion. This slows digestion. Soluble fiber is found in oat bran, barley, nuts, seeds, beans, lentils, peas, and some fruits and vegetables. It is also found in psyllium, a common fiber supplement. Some types of soluble fiber may help lower risk of heart disease.
Insoluble fiber is found in foods such as wheat bran, vegetables, and whole grains. It adds bulk to the stool and appears to help food pass more quickly through the stomach and intestines.
Benefiber is soluble fiber only with a prebiotic. Benefiber doesn’t bulk the stool.
Metamucil & Psyllium, which is in Metamucil, has both soluble & insoluble fiber. The insoluble fiber bulks the stool.
Benefiber helps to slightly slow the stool where Metamucil/Psyllium Husk is more likely to rush right through bowels especially if taken with lots of water. For loose stools Metamucil will bulk your stool if taken as a slurry in only 2-3oz of water. This is also why I recommend not eating or drinking for 30 minutes after taking Metamucil if bulking up loose stools is goal.
Citrucel (methylcellulose) is mainly insoluble fibers that are nonfermentable, so it's less likely to contribute to bloating and gas. Psyllium husk (Metamucil and Konsyl) is rich in both soluble and insoluble fiber.