Psyllium powder is ground down psyllium husks to produce a very fine powder. Psyllium is a source of soluble dietary fibre, it expands when mixed with liquid. It can help relieve constipation and diarrhea. Psyllium is used in gluten free baking, as the finely ground husks bind moisture and help make breads rise and less crumbly. You can purchase psyllium husk powder from a supermarket or make your own by using a blender or food processor to ground to a very fine powder.