There are so many different types of substrate, what are the reasons to choose one type of substrate over another, or is it all just personal preference?
There are two basic types of substrates for bearded dragons, there are benefits and downsides to both, and it comes down to what you feel is safe for your bearded dragon, and what you feel you can manage for cleaning.
In short, particle substrates allow the bearded dragon to dig, which is something they do enjoy doing, but gives a risk of impaction from ingesting the substrate. It can also be considered difficult, or annoying, to keep clean, and needs to be replaced at regular intervals.
Meanwhile non-particle substrate remove the risk of impaction, but will most likely require you to provide other means of allowing your bearded dragon to dig. Artificial surfaces can be difficult for bearded dragons to walk on, either catching their claws, or being too slippery to provide traction.
I have to admit, I have a personal bias against sand as I write this, but sand is regarded by many reptile enthusiasts as being a poor choice for a substrate because of its many health risks, that are viewed as outweighing its benefits.
Sand is the most common substrate being marketed as the proper substrate for bearded dragons. Because bearded dragons come from the desert, it's easy to market sand as a desert substrate. In truth, a bearded dragon's natural substrate would be a mixture of hard packed dirt, clay, and rocks.
Sand can be considered a bad choice for bearded dragon's substrate for the following reasons: 1. Bearded dragons are messy eaters, so if you feed them in their terrarium, they'll inevitably ingest some sand. Because sand is indigestible, it creates the risk of impaction, a medical condition where the bearded dragon's intestines are blocked, causing paralysis and death. 2. Bearded dragons "explore" with their mouths. Meaning that even if you don't feed them in their terrarium, the risk for impaction still exists. Mine will still lick things in his enclosure that have been there ever since I set it up. 3. Sand is dusty, which can lead to respiratory problems if the bearded dragon inhales it. Or cause infections if it gets into their eyelids. 4. This is dependant on the person taking care of the terrarium, but sand can be considered difficult, or annoying, to keep clean. If fecal matter is left behind, the sand will readily harbor bacteria, causing the terrarium to smell. If it is not kept sanitary your reptile to be exposed to a greater risk of infections/parasites.
On the other hand, damp sand can be one of the best substrates to use for a gravid female, as she will wish to bury her eggs.
There's a newer type of "sand" being pushed that is supposed to be good for bearded dragons. The idea is that if bearded dragons are going to eat some of the substrate, then it might as well have calcium in it to make it better for them.
The bad part is that it's not actually sand but calcium carbonate found in limestone and chalk, and is actually a leading ingredient in TUMs. The side-effects of this will mean that your bearded dragon will have a harder time digesting their food because of the effect it has in neutralizing stomach acids. And if the bearded dragon feels like it needs more calcium in its diet and eats more of the sand, the effect will only get worse.
For this reason, calci-sand should be avoided in favor of plain sand.
Included with the calcium-sand is sand that has been dyed different colors. The problem with the dye is that it permanently stains the bearded dragon's skin. I do not know of any health concerns that have been linked to the dyes though. My recommendation would again to stick to plain sand.
As I mentioned, a more natural substrate for bearded dragons is compacted soil. I've heard of people mimicking this substrate type by using a mixture of about 50/50 topsoil and sand (the kind you get for children's sandboxes).
The benefit of this is that the compacted dirt is less likely to get ingested, and even if it does, the dirt is less likely to cause impaction by itself, and it keeps the sand from clumping together, which is what causes impaction.
The downside to this substrate is, like all particle substrates, that it can be difficult/annoying to keep clean and needs to be replaced at regular intervals.
You can find substrate made from crushed walnut shells in some pet stores. This substrate Should never be used for bearded dragons. The crushed shells have extremely sharp edges, and will cause damage to a bearded dragon's internal organs if ingested.
This substrate is meant for tropical reptiles, because of it's ability to retain moisture. In a desert terrarium, where that amount of moisture isn't needed, the dry coconut fiber contains too much dust to be safe.
Wood chips pose a similar risk to bearded dragons as crushed walnut. While not as consistently sharp, they can still cause damage to a bearded dragons internal organs if ingested.
Reptile carpet is a simple alternative to particle substrates. It comes in a roll of felt fabric that you can lay down at the bottom of the terrarium. The positive side of reptile carpet is that it's easy to clean; you can simply take is out and rinse it off. The downside is that bearded dragons' claws have been known to get caught in the fibers.
Recently I've seen new forms of reptile carpet, that instead of felt, they've taken to simulating sand textures. Which would effectively eliminate the risk of the bearded dragon's claws getting caught on the carpet. My only concern would be the damage that the bearded dragon could do to the carpet, by attempting to dig at it, could require the carpet to be replaced every so often.
You can use paper towels, and then you wouldn't have to worry about the bearded dragon's claws getting caught, like you would with the felt carpet, but as soon a paper towel is soiled you're going to have to replace it. This can get fairly pricey depending on the cost of paper towels at your store.
Slate tile is what I personally think is the best substrate, seeing as it's the one I use.
Like other non-particle substrates, it's easy to clean, and has no risk of impaction. But, it also has the benefits of holding heat well, and it even helps keep their claws worn down naturally so you'll never have to worry about trimming them yourself.
Because you can purchase slate tile at your local hardware store, you can usually find many more varieties in colors than you would find for reptile carpet, and the colors look closer to natural substrate colors (you can probably find sand colored tiles if you prefer the look of sand).
Some people go so far as to add grout, I opted not to so that I could take the tiles out in order to clean them, but having grout does have the benefit of keeping dirt from getting in between the tiles. It's really up to you on which method you prefer.
I have found ground up corn cob (dried) that I found at bimart in the bird section to be a great substrate for my bearded dragons cage. ( I have a open cage wood and chicken wire wrap so air is always circulating. ) its easy clean up cause it acts like kitty little absorbs smells well. When wet it plums up and disolves ( i tried it popped a few in my mouth to test) if the dragon eat it it won't harm him. No flavor to them so my dragon doesn't eat it. Although he did try some at first. After a few month just remove the cobs trash them or composite them and put fresh cob in..