This is from another forum and is well written.
There are substrates that are good to use and some that should be avoided at all costs.
Good Substrates
NEWSPAPER. Double check what kind of ink your local newspaper uses- most use soy-based inks (good)
KITCHEN TOWEL. This is a great substrate for babies - it's what I use until they reach 10" long
NON ADHESIVE SHELF LINER. Can be used by itself or with paper towels, carpet or a combo of them. Wipes up easily and has become very popular in use for young dragons. Many owners are using this then adding the carpet or paper towels as they grow older, including a sand box or sand pit for adults.
WASHED PLAY SAND. Once your BD reaches 10" you can safely put it onto particulate substrate- just make sure the brand of play sand is not too dusty - that's why you should get washed
RABBIT PELLETS. Several reputable Breeders use this as a substrate. It's essential that you remove faeces as soon as possible if you are choosing this
CAREFRESH. Ronnie Buck of AB HERPS, has experienced good results with this
SAND/PEAT or SAND/SOIL mixture---more diggable and seemingly more like their native soil than pure sand is, although I personally keep the sand dry so diggability is not an issue. Make sure that the soil is clean- I recommend baking it first.
BAD Substrates!!!!!!!
The following are bad for one main reason - impaction. A lot of stores may try and tell you that they are suitable, they may even be using them themselves, but they are wrong. Each of the following have proven to cause impaction and death to Bearded Dragons (as well as other reptiles) and should be avoided like the plague. If you suspect impaction in your dragon, post on the list and members will help you with some information
CORN COB. It's hard to pick which of the following is worst but I think this one is it! Hard, large and indigestable for Beardies
WALNUT SHELL. It looks harmless enough, but the edges are very sharp and it could kill your dragon very easily. There have been documented impaction deaths in BD's from this. Also goes under a variety of brand names, so check package labelling carefullt before listening to and buying from pet stores.
CALCISAND. The problem with this product is twofold. First, they like the flavour of it and may eat it if they are lacking adequate calcium in their diet. Second, it can clump and form an indigestible bolus in their digestive tract.
REPTI BARK is also a no no - it is very fibrous and could easily end up causing impaction and has been known to end up lodged in the vent.
Any of the wood shaving like cedar or pine should also be avoided - cedar had dangerous aromatic oils and pine can get impacted if ingested.
ORIGINAL LIZARD LITTER made from the kenfa tree and JUNGLE BLEND or something like that. It's real fibrous and also can cause impactions. It may be the same thing that claims to be made of 100% renewable resource coconut fibers (pulverized), and "exists as an alternative and digestive material to peat moss, vermiculite, sand and soil". Frankly I doubt the digestibility claim- especially for Bearded Dragons, which have short digestive tracts
ONE OTHER WARNING, BE VERY CAUTIOUS USING BLEACH ON THEIR ENCLOSURE OR FUNDISHINGS, in not rinsed really well, the heat from their lights can cause toxic fumes from the bleach