In my experience, I do not care to use stiffen stuff and here is why:
1. It does cause the bows to be extremely hard.
2. The bottle clogs up very easily.
3. Kind of expensive.
4. Very hard to find.
Therefore, I have resolved to using aerosol hairspray. It works perfect. It puts a light coat onto the bows to keep their shape but not too stiff and it is really cheap easily found in all stores and you never have to worry about the bottle clogging up.