Medibed is a chopped straw thats OK (and is treated). Do not use Nedz, it has added Eucalyptus. Chaff (chopped straw and hay mix) is OK and I sometimes use that. Barley Straw is lovely and soft too. But, always make sure hay is available for them. Other straws are too harsh as Michelle says so if in doubt about the type of straw then don't use it.