Sawdust on bottom level. Terrace shelves to prevent falls. If their cage is kept outside it will need more enclosure to prevent drafts and fear from approching predators. Wood can be places on top and sides. If you have enough chinchillas so they can cuddle together, the temperature can drop much lower.
Branches are fun and make the cage easier to clean because droppings and urine fall to the bottom.
Soft Pine, on the other hand, is best. Here is the other Mary-Ann Holden page.