Whey Protein Isolate
The isolate version we use does not contain casein or lactose, which are the components of milk that some people are allergic to. Very few individuals are sensitive to whey protein isolate.
After research, we eliminated soy as a possible protein base. Though it is a complete protein, it has an unpleasant, beany taste that must be masked. Second, and possibly more important, is that soy contains various enzymes that inhibit the digestion of proteins, fats, and carbohydrates. These anti-nutritional enzymes actively prevent you from getting nutrition. Soy protein is flexible in its texture and has a low cost, but the other attributes make it a poor choice for a general protein bar.
We researched using egg white, which is a widely available, complete protein and has a digestibility almost equal to whey protein. A major problem with egg white is that the sources of egg white protein process their powder in different ways. One batch might absorb a certain amount of water while another will absorb much less. It was this inconsistency that led us away from egg whites.