Bedding

Bedding can be newspaper, wood shavings, other paper type shreds, tissue paper, corncob and others. Bedding provides a material for hamsters to burrow and sleep in and it also absorbs the hamsters' urine.

Get one especially for pets - don't be tempted to try other sources (commercial timber is treated with chemicals).

Other bedding like sawdust and soil are unsuitable as these are too fine and could also damage your pet's health. For nesting material, use solely Kleenex. Other kinds of nesting material can be ingested and can kill them.

There have been reports that pine and cedar bedding are bad for our pets' health. Cedar and pine shavings have been blamed for causing respiratory problems in small mammals kept in them. There are a few articles at The American Fancy Rat and Mouse Association (AFRMA). I've not seen other associations with information on this and if you have, please send me the links.

Newspaper
Some owners also use newspaper but in my experience, this isn't such a great idea. My syrian dug it up and pushed it around, so that it wasn't much of a bottom cover. It doesn't soak up liquid very well and you end up having patches everywhere, which doesn't look or smell too good. There are also concerns that newspaper ink might be harmful to your pets. Burrowing is also limited. Some shred the papers but others do not. On the other hand, I've heard of people using newspaper when their pets are allergic to other beddings.

Some other alternatives - link of exotic pet care at about.com corncob, aspen, hay, tissue paper