This is one of the top questions many chicken owners ask themselves in regard to nesting boxes. The truth of the matter is that hens are all different and you might find that they respond better to one material or another, so it's worth testing out a few options in the early stages and seeing what they like best. Shavings and sawdust are popular options due to their affordable nature, but they can get dirty quite quickly. Shredded paper is cheap too and easy to replace. Straw and hay are good options but need to be changed regularly due to the build-up of dirt and bacteria, and grass clippings can be very comfortable for the hens, as long as the grass has no chemical treatments on it. Overall, the best choice depends on how much you want to spend, how your hens react, and how often you plan on cleaning the boxes.