Excipient (pharmacologically inactive substance)
What is it?
Polycarbophil (FiberCon, others) is a bulk-forming laxative that increases the amount of water in your stools to help make them softer and easier to pass. Polycarbophil is used to treat constipation and to help maintain regular bowel movements. Polycarbophil has also been developed as a kind of pharmaceutical polymer with superior bioadhesive properties used in the field of controlled drug delivery systems. It could be used as a highly efficient thickener, bioadhesive agent, suspending aid and emulsion stabilizer when dispersed in water or other polar solvents. These exceptional utilities of the polymers result from their hydrophilic nature.  
 Zhu Z, et al. The development of polycarbophil as a bioadhesive material in pharmacy. Asian Journal of Pharmaceutical Sciences. 2018;8:218-27. http://www.sciencedirect.com/science/article/pii/S1818087613000317