The Soybean Hulls provide much needed nutrients to your ideal substrate mix.It is possible to grow mushrooms on many substrates but if you want the best you want soybean hull pellets and oak pellets for the ideal mix. If you are making your own ideal substrate mix you know there are two key ingredients.100% Oak Sawdust and Soybean Hulls.These pellets are easier to handle, move, mix, and measure than loose hulls.They also break down just as the sawdust does from hardwood pellets by just adding moister and mixing.