How do rice hulls work?

I never used them, but want to try them. I'm having a hard time visualizing what they do in the mash exactly.
they are supposed to act as a filter right? So wouldn't it be best to but them on the bottom and the grain on top? I read that people just throw them in with the grain. How would they be beneficial if they are in the middle of the mash or on the top?

Also how much do I use?

They act as a filter but also help to reduce dough balls throughout the mash. Particularly helpful in mashes containing wheat since it's notorious for sticking together. I just stir mine in and that works for me. As for how much to use. I use about a half a bag per 10 pounds but maybe more for large amounts of wheat. Hell the stuff is dirt cheap use as much as you want!

Ah. Thanks! getting rid of the dough balls makes sense.

If you are using rye in your recipe, rice hulls are needed. Rye gets sticky too.

They add 'fiber' to the mash. Its otherwise useless husk material that helps space out the crushed grain kernals so that the wort can flow through the mash bed easier.

You do want to mix it into the entire mash while doughing in the other grain. I typically add the hulls first into the water to help wet them. They do tend to be slow to get wet. With them in the water, I then dough in the actual mash grist while stiring vigorously. That incorporates the hulls fairly well in the mash.

Thanks for all the tips! Mystery solved. Seems super easy.

Here check this out.
http://www.brew-dudes.com/rice-hulls/517