Natrasorb is a modified wheat starch used in high-load oil products whereby one wants to control the greasiness and/or a matte finish is desired (makeup, oil-control powders, etc.). Natrasorb Bath is a modified tapioca starch. It is hydrophilic which means that once it is in contact with water it dissolves, releasing/dispersing the oils. It is commonly used in bath powders, bombs, talc. Edited to add: Natrasorb Bath and the tapioca starch you can purchase in the store are also two different things. As a comparison: NB is like refined table salt and tapioca starch is like rock salt. They feel different and there is definitely a difference in how they perform in your B&B products.