Polyvinylpyrrolidone is a vinyl polymer that is soluble in water. It is also inert and not absorbed by the body. This is probably why it is used in the making of hard capsules. You can find out more at the link from The School of Polymers and High Performance Materials at the University of Southern Mississippi. For grades and specs and prices, go to www.google.com and do a search. You will find many manufacturers. Polyvinylpyrrolidone is made by joining lots of vinylpyrrlolidone molecules together into a long chain. This is also explained at the link above.