The primary difference is the source of fiber. The Fibermend uses a fiber called “hydrolyzed guar gum”–basically, you take regular guar gum and break the chains into smaller pieces. The result is that the fiber no longer gets thick and goopy
The Medibulk, on the other hand, uses different fibers (psyllium, prune, and apple pectin), all of which gel when exposed to water.
Both are soluble fibers, and nearly all soluble fibers (if not all) “gel” when exposed to water–they absorb water, so they make whatever they’re mixed into thick. The shorter pieces of hydrolyzed guar gum make it so it doesn’t react the same way, though it still retains all the other benefits of soluble fiber!