Fiber supplements come in several different forms. Psyllium husk is a frequently used type of soluble fiber. Psyllium absorbs water, and swells. This helps to relieve constipation by providing bulk to form a stool that is easily passed.
Methylcellulose is another form of dietary fiber. Methylcellulose works in the same way as psyllium husk. It is a good source of soluble fiber.
Methylcellulose and psyllium husk are often taken mixed with water or juice. They also come in tablet and chewable forms. It may take some experimentation to find the right type and dosage of soluble fiber for you.