One of the oldest and most traditional materials for making mari for is komegara - which literally translates as "rice shell" or "rice skin" - what we call rice hulls.That is just what it says it is - the outer husk removed from the grains of rice when it's polished (the outer husk that  makes brown rice brown). They are becoming easier to find with the advent of home-brewing and wine since they can be used in the fermentation and/or filtering processes.

        Rice hulls are easy to use, and "mold" (almost like a good snowball) when making the mari, which makes it very easy to construct a round mari as you wrap. A rice hull mari has a wonderful "in-hand" feel - just a little heft to it but not too much. Most folks that try rice hulls generally end up being converted to them for being the best mari core material (considering they have been used in Japan for hundreds of years for this, we probably shouldn't be surprised).

        Place the desired amount into a small baggie, stocking, or even wrap in plastic wrap, and then mold into a ball as you begin wrapping. They are very malleable (easy to shape and mold) because of their size and composition. A pound of rice hulls is about one gallon in volume. About an ounce of rice hulls fits nicely into a sandwich baggie or stocking (about 1/2 - 3/4 cup, give or take) and results in a mari about 2 1/2 to 3 inches in size depending on your wrapping. A canning funnel (wide neck) is a great help in filling a stocking or sock.  A pound of hulls can yield about 12 to 16 mari of this size (BUT -  this also depends upon your wrapping habits. This is only to give a rough idea of "how much does what" - it will vary with each person depending on your bagging and wrapping techniques. The main point is that rice hulls "go a long way", relatively speaking, and you probably don't want to buy into say, 50 pounds of them (unless you are divvying up with buddies)).

       Rice hulls purchased from brewing supply sources are a cleaner product, since they need to meet food-industry standards. They have a virtually indefinite shelf life as long as they are kept dry (though they are dry and "flammable" - like paper or wood, so store accordingly). Those sold for garden mulch can have much more dirt and other "contaminants" (including ones that walk and/or fly) as well as being damp, which can lead to rotting. I urge you to avoid these, since they really are dirty to start with, and also are in danger of rotting inside the mari which destroys your effort and work. If you do purchase komegara from a garden supply source, be sure to store them in the garage or suitable place until you treat them. One of the best (though absolutely not foolproof) ways to take care of critters,  and also dry them out,  is to put a batch in the microwave. This will both dry them and kill off any bugs. Some people store them at room temperature, and others will bag them and put them in the freezer just to be sure all "things" are taken care of and stay that way. There are several brewing suppliers listed in the Supplies section of Temarikai.com and it's suggested that you purchase food-grade hulls just to be safe. Brewers also tend to sell "human" quantities - such as 5 or 10 pound batches (which is still a significant amount of rice hulls).

       If you use noisemakers in your mari core, you will want to be sure to use a small box or other "solid container" to house it, since anything with openings will allow the hulls to fill it, which will muffle the bell or noise. When bagging hulls or making your mari, use a little care since they are lightweight and will "blow around" - be sure to not be in a drafty place or (or have a ceiling fan on. Ask me, I know....)