Rice hulls are used as an aid when mashing high protein mashes such as Wheat, Oats & Rye.
Rice Hulls greatly help in avoiding a stuck mash where your mash will not recirculate and also aids in avoiding stuck sparges. This is where your sparge water will not drain from your grain basket, bag or through a false bottom.
The best way to use rice hulls is to put in a few handfuls when you mash in and combine with the rest of the grist. This will help provide some channels for the mash or sparge water to flow freely through the grain.
It is advisable to use rice hulls in up to 5% of the grain bill for wheat beers or other adjunct laden mashes.