Hemp is the ultimate laying box medium.  As well as the other benefits listed below it is also not hollow like hay/straw which is a perfect habitat for lice and mites.  Hay/straw starts to rot when it gets wet and is not suitable for laying boxes.
 
Dust Free
Springy Insulated Bedding
Fully Sustainable & Renewable
Super Absorbant
Great Garden Mulch When Soiled