The most common types of filament for 3D printers are ABS and PLA. And while they are quite similar, they each have their own unique features that might cause you to choose one over the other. Here are a few key points on how these filament materials differ.
Without getting to much into the science of them, here is a brief and completely simplified explanation of what the two common plastics are.
ABS - Acrylonitrile butadiene styrene is a petroleum-based plastic made by polymerizing styrene and acrylonitrile in the presence of polybutadiene.
PLA - Polylactic acid or polylactide is a thermoplastic aliphatic polyester derived from renewable resources, such as corn starch; tapioca roots, chips or starch; sugarcane or sugar beets.
Both ABS and PLA are thermoplastics, meaning they become soft and can be molded when heated and they return to a solid state when cooled. This process can be repeated over and over with these plastics and it is a big part of the reason why thermoplastics make up the majority of the plastic you interact with in your daily life.
Although many different thermoplastics exist, few are used for 3D printing. To be useful for 3D printing, a material has to be easy to turn into the raw printing material called plastic filament, it has to easily bind to itself during the 3D printing process, making for aesthetically pleasing and physically accurate parts, and it has to be sturdy for robust printed products.
Both ABS and PLA can be turned from a pile of plastic pellets into a uniformly dense, bubble-free and consistently sized rod of plastic filament quite easily. Most thermoplastics can go through this initial phase of plastic filament creation easily and ABS and PLA act essentially the same for this process.
It’s after this process is complete and you move onto the actual 3D printing process that ABS and PLA start to show their differences and where you might start leaning toward one over the other.
Both ABS and PLA should be kept in a sealed container to prevent them from absorbing moisture from the air if storing them long term. They will not be ruined from sitting on a bench in your shop for a week but if they are exposed to a humid environment for a long period, it will have adverse effects on the printing process and the finished products.
ABS - If ABS picks up too much moisture from the air, it tends to bubble and might spurt from the tip of the printing nozzle. This, obviously, will not only make the printed product look bad but can affect the accuracy of the part, its strength and the spurting can also cause stripping or clogging in the nozzle. You can dry ABS by using a source of hot, dry air like a food dehydrator.
PLA - When PLA absorbs too much moisture, it poses additional problems to the bubbles and spurting from the nozzle. You might notice a discoloration and reduction in 3D printed part properties, as PLA reacts with water at high temperatures and undergoes de-polymerization. Like ABA, you can dry PLA by using something like a food dehydrator but doing this can alter the crystallinity ratio in the plastic, which could lead to changes in the extrusion temperature and other extrusion characteristics. However, for most 3D printers, this isn’t a major concern.
ABS - When printing with ABS, you may notice the odor of burning plastic. Although some complain about the smell, it is usually not unbearable and can be easily counteracted by ensuring proper ventilation in the printing space and using ABS that is pure and free of contaminants and heated to the proper temperature while printing.
PLA - Since it’s derived from sugar, PLA tends to give off an odor that can be comparable to a semi-sweet cooking oil. Although not exactly pleasant, many people prefer its odor over that of ABS.
Both plastics are quite capable of rendering parts that accurately conform to the dimensions specified, but there are a few points worth mentioning that may cause you to lean one way or the other.
ABS - On an unheated printer bed, ABS can curl upward when it comes into contact with the bed. The printing surface should be heated and it should be smooth, flat and clean, which helps eliminate this issue. Some have found that applying a mixture of ABS/Acetone or a shot of hairspray to the printing surface prior to beginning the printing process helps counteract the curling issue.
Fine features on parts that have sharp corners (gears, for example) will often see a slight rounding of corners. A fan that cools the object slightly while it’s being printed can improve the sharpness of corners. The caveat with using a cooling fan, though, is that too much cooling can reduce adhesion between layers, which can lead to cracks in the finished product.
PLA - PLA is much less prone to warping and you can successfully print without a heated printing bed. Many people, when printing with PLA, use common painter’s tape as a print surface. Sometimes having a completely unheated printer bed can allow the PLA to slightly curl up on large parts, but this doesn’t always happen.
PLA goes through more of a change when heated and becomes much more liquid than ABS. If you cool PLA while it’s printing, you can get much sharper details on corners without the risk of cracking or warping. This increased flow while printing can also lead to stronger binding between printed layers, improving the strength of the printed part.
ABS - In general, ABS is a strong plastic and compared with PLA has mild flexibility. This flexibility makes it easier to work with interlocking or pin connected printed pieces. ABS can be easily sanded or machined and is soluble in Acetone, meaning you can weld parts together using a drop or two of Acetone. You can also smooth and create a high gloss on ABS parts by brushing them with Acetone or dipping full pieces in it. Prior to being colored, ABS is a soft, milky beige.
Those with mechanical uses in mind often prefer ABS for its strength, flexibility, machinability and higher temperature resistance.
PLA - PLA is created by processing plant products such as corn, potatoes or sugar-beets and is considered a more environmentally friendly plastic compared to the petroleum based ABS. It is primarily used in food packaging and containers and can be composted at commercial composting facilities (not in your home composting pile, however). It is more rigid than ABS and can be more difficult to work with in complicated interlocking assemblies or parts with pin joints. Printed objects will generally have a glossier look and feel than their ABS counterparts. Although it takes a bit more work, PLA objects can be sanded and machined. Perhaps the biggest drawback to PLA is that it has a lower melting temperature, meaning if you leave your 3D printed object in a hot car for a day, you will likely find that it has been deformed in some way. In its natural state, PLA is transparent and can be colored to various degrees of translucency and opacity.
This is a quick recap of the aforementioned points and a broad comparison of the two filaments.
ABS - ABS’s strength, flexibility, machinability and higher temperature resistance make it the preferred choice for engineers and professional applications. It’s burning plastic smell deters some people, as well as its petroleum based origin. Because it needs a heated printer bed, some 3D printers simply won’t be able to reliably print with ABS.
PLA - PLA’s wide range of available colors and translucencies, plus its glossy feel and look often make it the preferred choice for people who print objects for display or for small household uses. Some people also choose it because of its plant-based origin and its semi-sweet odor during the printing process. When cooled properly, PLA generally allows for higher maximum printing speeds, lower layer heights and sharper printed corners. This, combined with low warping on parts makes it popular for home printers, hobbyists and schools.
If your printer is capable of printing with both ABS and PLA, it would be a good idea to start off with some of both and experiment to see which one is your preferred choice. Your preference might switch from project to project, too, as one’s properties might make it a better choice over the other depending on what you’re printing at the time.