Traditional hydrocolloids include flour, cornstarch, and Wondra flour. As anyone who has ever used flour to thicken a stew before knows, you have to quick flour with oil into something called a roux before you can use it as a thickener. That's because flour can hydrate in both cold and hot water and can quickly form lumps. Wondra flour is essentially normal flour that has been pre-gelatinized: that is, it has already been hydrated, then that hydrated product is dried back into a powder. But, since the granules are already hydrated, it doesn't form lumps.
In addition to these hydrocolloids, we also include with them any thickening products that are made from flour or other hydrocolloids, such as bread or tortillas.