Fiber in general will do that. Is there something special about Glucomannan?

I find that it's more palatable and mixes better than psyllium.
It has a clean taste, not like eating saw dust.
I believe it bulks more than either psyllium or inulin, yet causes
me less intenstinal discomfort.

Actually it can be bought in noodle form for cooking too - it's been used in Japan for centuries. Called Shirataki noodles.
Konjac Foods - Pure Fiber Zero Calories Pasta