outdoor carpet is basically astroturf, that plastic short pile carpet you can get at hardware stores for balconies etc. It's pretty cheap but some can be a risk. If the pile is very short and there are no unraveling strands, it's alright. It also needs to be washed and sterilized regularly to prevent bacteria buildup (once a week is good, just buy two or more pieces big enough to fit your tank and swap them out). Reptile carpet is pretty much the same thing, though, if I recall correctly, it doesn't have much of a pile but pretty much the same cleaning method as outdoor carpet.
other substrates you can use are non stick shelf liner (duckbrand seems to be the one of choise, just make sure it is non porous), plastic tablecloth (something i have used myself with my bearded dragon, works great. easy to spot clean, just toss it out once a month and put in a new one) ceramic tile can also be used but will either need to be sealed into the bottom of the tank or cut to fit snug to prevent worms/crickets and debris getting in between the tiles.
Some people use wheatbran but I don't recommend it. If it gets damp at all, it molds very quickly. It also can harbor various kinds of grain eating bugs, which get all over your tank and house. Not to mention its easy for crickets and other insect foods to vanish in. Mealworms/superworms can burrow into it and next thing you know you will have these big black beetles running around the cage (at least till the dragon eats them, with isn't too much a concern with adults but could be a danger to young dragons).
Of all the other loose substrates, washed sifted playsand is the best. There is a chance of impaction but it's not as bad as other similar appearing substrates (ie calci-sand, reptile litter, mulch etc)
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PHLdyPayne