The great substrate debate
Substrate is the general name for the material placed on the floor of reptile enclosures. Depending on who you talk to, there are many different, good, bad (and just plain ugly!) substrates that you can use in a reptile enclosure. This article will describe a number of different cage substrates that are commonly used, with both positive and negative points being mentioned. Where possible, a photo of the substrate is included.
However, the final decision on which substrate is best for your situation can only be made by you - taking into consideration the ease of cleaning, availability, looks and what occurs in the animal's natural environment.

A warning.
If you choose to use a loose substrate (e.g. recycled paper pellets, gravel, sand etc.) it is suggested by most keepers that you do not feed your animal in the cage with the substrate present. The accidental ingestion of substrate particles has the potential to cause health problems in your animals, ranging from decreased nutrient absorption, to a fatal impaction (intestine blockage). It is strongly suggested that a large feeding bowl is used (for lizards) or removal of the substrate/animal is considered during feeding (snakes).
No matter what type of substrate you choose, you need to be sure that you do not create a fire hazard, especially considering most reptile enclosures are heated. Special care needs to be taken when using any substrate on top of a heat mat or hot box, as a build up of heat in any situation can cause a fire, which needless to say is a Very Bad Thing.

Nothing Obviously, this is the easiest type of substrate to have in your enclosure. It doesn't necessarily look great, but is easy to clean just by washing/wiping out the enclosure. If you put nothing on the floor of your enclosure, your animals will be urinating and defecating directly onto your enclosure floor. Also, most keepers try to replicate a "somewhat natural" environment for their animals - needless to say, most keepers choose to use something rather than nothing as a substrate.
Paper Paper is easy to use as a substrate. It's placed on the bottom of the enclosure, with the enclosure's furnishings on top, and, when soiled, it is removed, tossed and replaced. This is usually done weekly or bi-weekly. Paper doesn't look natural, but is extremely easy and fast to change, and is commonly used by keepers with large collections. Newspaper (or newsprint) is commonly used, although it has been suggested that the ink could be toxic to animals. For this reason, a number of keepers use 'butcher's paper', or unprinted newspaper. This also can look better than old news sitting on the bottom of the enclosure. Newspaper or butcher's paper is also often used in conjunction with another substrate, being placed underneath to protect the enclosure floor, and enabling easy removal of mobile substrates by just picking up the entire sheet(s) of paper and bundling up the substrate on top.
Recycled paper pellets (e.g. Breeders choice) A step up from paper is to use recycled paper pellets, which are made for use as kitty litter. As such, they are very absorbent, and while they don't look completely natural, they can look quite good in an enclosure (kind of like a grey gravel), and are extremely easy and fast to change - the used pellets are tossed out or used in the garden as mulch. Because of this, these pellets are another substrate commonly used by keepers with large collections. It is important to note that not all the pellets will need to be changed on every occasion - soiled pellets become obviously discoloured, and swell to around twice their initial size. The soiled pellets can easily be removed and replaced with new ones - a full substrate change is not required. However, it is still suggested that a full substrate change (and enclosure clean) is conducted every one or two weeks. These pellets will break down over time, so it's important to remember that simply "spot cleaning" will not do. Silverfish are also attracted to these paper pellets, so if you don't clean your enclosure for a while you might end up with a healthy colony of these insects. These pellets can be quite dusty, so it's a good idea to shake out the dust (perhaps by putting them into a large garden sieve) before using them in an enclosure. These pellets come very dry, and because of this they are very absorbant. When you first add them to an enclosure, they tend to lower the enclosure's humidity for the first few days, by absorbing all the water from the air. This can be a problem if your animal is coming up for a shed. One way to avoid this problem is to leave the required amount in an open tray for a couple of days - the pellets will abosorb water from the air in the room, and as such will not dry out the air in your enclosure as much when you add them. These pellets can also easily stick to anything wet, including food items. It's recommended that you don't feed your animals on this substrate, as invariably some pellets will get ingested. Whilst there have been no reported side effect of accidental ingestion, it is best that the risk is avoided. If dry pellets are ingested, it's conceivable that they'd swell up in the animal's stomach, which (needless to say) could be a problem. It has been suggested that these pellets will just break down in a fluid medium, but nevertheless, recycled paper isn't a 'normal' food item for any Australian reptile!
Gravel Aquarium gravel is also commonly used, especially by keepers from the Southern Australian states. It looks more natural than paper, but is harder to keep clean, as the gravel should be removed regularly and washed, because wastes can easily get hidden in the gravel. See the hygiene page for more information. Small gravel pieces can also become lodged in between scales in snakes and lizards, causing problems. You should not feed your animals on a gravel substrate, as the gravel can be ingested accidentally with the food item, and cause impaction in the intestine. This can be a fatal condition. Gravel is also harder to keep warm than substrates such as paper, so you'll need to take this into consideration when deciding on your heating method.
Sand Sand is another commonly used substrate that looks very natural. Like gravel, it too should be removed and washed on a regular basis (see the hygiene page for more information). Sand is commonly used for desert animals such as Adders and Dragons, and can make for a very spectacular setup. You need to be cautious about feeding your animals on sand, as it can be consumed accidentally, and cause problems (impaction) in your animals' gut. Some digestable sands are available (normally consisting of some form of calcium), but the jury is still out as to whether or not the high cost of these substrates makes them worthwhile.
Leaves/Bark This is another very natural looking substrate suitable for a wide variety of species. Leaves and bark can easily be obtained from backyards, and crushed to form a litter for the base of the enclosure. Like branches and rocks obtained from a natural setting, you must assume that it is carrying insects/parasites/chemicals that could possibly harm your animal. Make sure you obtain clean leaves/bark and that you disinfect and dry them thoroughly before placing in your enclosure. See the hygiene page for more information. There are a number of commercially available bark/leaf/bush floorings that have been disinfected and cleaned prior to sale. Be sure NOT to use bark/wood chips that contain treated pine (green coloured). This is toxic due to the chemicals used in the treating process, and is not suitable for use as a substrate.
Outdoor Carpet and Fake Grass ("Astro Turf") Squares Some keepers use carpet designed for wet area applications (such as boats) which is usually a synthetic with no pile and a bonded waterproof backing. It looks better than newspaper, especially in the brown and green colourations. Despite an initial cost, it is inexpensive as it can used over and over again. Keepers who use this usually have two squares cut for the base of their enclosure, and when cleaning the enclosure, swap the squares, the old one then being washed vigorously in soapy water and/or a disinfectant. "Astro turf" is very similar. It's the fake grass material used on the surface of some tennis courts and indoor sports arenas, and looks semi-natural. A word of caution - some keepers have reported the hemipenes (the male reproductive organs) of some snakes becoming prolapsed as a result of using "Astro Turf". Bearded Dragons are also reported to loose their claws by catching them in this substrate.
Crushed walnut shells Often suggested by American sites/books/people as a substrate to use with Bearded Dragons, but this should not be used! While they look natural, crushed walnut shells may cause impaction of the intestine when eaten, and can kill your animal. Don't use it.
Viewer Comments Here are some comments made by other reptile keepers from around the world. If you've got something to add, please let us know. Raffaele says: "Torn up egg carton substrate - it looks better than newspaper, readily obtainable, easy to replace, super absorbant and you know it's safe because it's designed for a food product. And reptiles love it. It gives them security as they can hide under the torn pieces. Gravel sucks - it's too noisy. Try sleeping with your lizard burrowing in gravel all night! And sand sucks as well. It makes your reptile stink and look like a little pig, especially when it's jumping in out of the water every 10 minutes. Sand acts more like a batter than a substrate." kerri from Nottingham, England, warns: Small gravel bits can become stuck under snakes' scales which can (obviously) be a problem. cam from Mt Isa, Qld, says: "I have been using wood shavings as a floor covering. This was sugested by my local pet shop. They use this for their mice, and some of their new snakes. I have found this to be good.............. so far." Julie says: "I have two central bearded dragons and have used many different substrates for an indoor enclosure, and always on the look out for new ideas regards hygiene, ease of cleaning and safety features. Finally I tried lino linoleum and have found this just great and would not use any thing else." Beau says: "I have found that using newspaper and fake grass creates a better enviroment for your animal to live in as they come in to contact with two different surfaces as they would in the wild. I hope this helps any one having troubles deciding what to use for a substrate. By the way I only use this in my python tanks and i use sand in my dragon tanks."

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