If you didn’t already know it, Acrylonitrile butadiene styrene (ABS) and Polylactic acid (PLA) are two of the most popular filament materials used for fused deposition modeling (FDM) 3-D printing today. Using one rather than the other comes down to various attributes of the material and, in some cases, personal choice. I have printed with both materials, and found positives and negatives for both. For my use, I find that I more often use ABS due to the characteristics of my needs, but I also use PLA from time to time.Maurizio Pesce CC BY 2.0Maurizio Pesce CC BY 2.0

There are a few material characteristics that can help you decide what to use and when. To start, I want to point out that not all filament is created equal. It is possible that some brands of filaments will cause more issues than others. I would recommend reading user comments before making any filament purchases to find out which brands other people have found successful. That being said, the most important factors are strength, temperature range, printer capability, post processing and environmental issues.

The strength and hardness required of the finished part

ABS is a more durable material, provided you have your printer set up correctly, as the layer to layer bond strength is its biggest weakness for 3-D printing. The toughness property of ABS is largely due to a tendency to flex instead of crack under stress. This toughness is in contrast to hardness, which is essentially a measure of how stiff a material is. The toughness of ABS can be a great benefit if you drop your finished part since in most cases, an ABS part will bounce, while a PLA part may crack or shatter. It is possible to improve the hardness of an ABS part — while sacrificing some of its toughness — by post processing it with the vapor treatment discussed below.

PLA tends to produce very hard parts that do not flex very much. This can be a great thing for some applications where flexibility could be a problem. I tend to consider the strength of a finished PLA part in similar terms to that of a ceramic part, just slightly less rigid. PLA parts can be very strong, and hold an edge so long as you don’t apply too much force on them. You would not want to hit a part made from PLA with a hammer, as it would likely shatter. However, PLA does not expand and contract as much as ABS does due to temperature, so if dimensional tolerance is very important, PLA would be the better choice of the two.

The temperature range of the part

ABS has a wider temperature range compared to PLA. ABS is typically extruded at around 230 degrees Celsius, although the glass transition point, where it begins to melt, is around 105 degrees Celsius. 230 degrees Celsius isn’t that hard for most 3-D printer hot ends to achieve, but that heat is not the only consideration necessary to successfully print with ABS. The glass transition point is important because it represents the maximum temperature your finished part can experience without damage.

The temperature range of PLA is lower than ABS, with a typical extruded temperature of around 190 degrees Celsius and a glass transition temperature around 60 degrees Celsius. This temperature range means that PLA could melt in a hot car or in the sun on a hot day. As PLA begins to melt, it will become more like a gummy candy than a rigid part. This is a very important factor of the material as it limits the use of the part. Luckily, I have not experienced a part that melted on me, thus far.

The 3-D printing machine available, and its capability

Not all machines can print with both ABS and PLA. Many machines can print with PLA, but will not work with ABS, and some commercial machines have been designed with ABS and other higher temperature materials in mind, making them incompatible with PLA. When in doubt, you should always consult the information that came with the machine or parts used to build it.

Since most hot ends can reach the temperatures required for ABS, the big difference is whether the build plate is heated or not, and if the printer is enclosed. ABS has a tendency to curl as it cools down, which causes parts to warp and become detached from the build plate. To help keep ABS parts from warping, the build plate is heated typically to around 90 degrees Celsius for ABS, although problems can still occur if the room is cold or if the area surrounding the print is breezy. Many printers designed for ABS have the print area enclosed so it will hold in heat and keep breezes at bay. For the most part, as long as the printer has a heated bed and an enclosed print area, you can expect a successful ABS print. If your printer is lacking the necessary hardware to print in ABS, it is not worth trying to use it. For some printers it may be possible to upgrade them and add the necessary hardware.

As I mentioned, PLA works in most printers that can successfully print ABS; however, PLA is less forgiving to hot end temperature fluctuation. PLA is not as self-lubricating, so some printers with all-metal hot ends may have trouble with jams. In some cases, jams can be alleviated with the use of a small amount of oil, but this should not be necessary if the printer is designed to use PLA. PLA doesn’t shrink very much when it cools, meaning it is less likely to stick to the build plate. As a result, intentionally sticking a PLA part to the building plate can be an issue, but it can normally be resolved using painters tape or glue, rather than requiring additional hardware. Another option utilizes a heated build plate, heating it to 60 degrees Celsius to help make the PLA stick, but this isn’t absolutely necessary.

Post finishing

Creative Tools  CC BY 2.0Creative Tools CC BY 2.0Vapor treatment for an ABS part is a common post processing treatment that consists of exposing it to acetone vapor. Acetone is a readily available solvent for ABS, and it will begin to melt the outer layer of the part, so that once it dries the chemically melted layer will be bonded. Vapor treatment give parts a smoother look, removing the layer effect, but it also removes some of the detail. As mentioned above, the will make the part harder and less flexible, but that it will still not increase the hardness to the level of a PLA part. Other post processing, such as the removal of support material, may be more difficult with ABS, but it does not normally present a significant challenge.

PLA is not soluble in acetone, but it is soluble in other less-common chemicals that can be attained online. While it is often not necessary to smooth a finished PLA part, it is something to consider when deciding which material to use. It is also possible to smooth PLA with heat from a source like a heat gun. This process must be done carefully, but it mainly consists of heating the part with hot air until it begins to melt the outer layer, then letting the part cool again. Personally, I found it difficult to achieve satisfactory results when smoothing the part with a heat gun.

Environmental concerns

ABS is not the most environmentally friendly material, and it is known to give some people headaches when they are printing with it. Generally speaking, it is not a good idea to breathe the fumes produced when printing, but it is worse to breath in the fumes from ABS. ABS is not biodegradable since butadiene is a petroleum hydrocarbon. ABS is a very common plastic used in many car parts and other plastic molded parts are used everyday.

PLA is structurally weaker, but it also more environmentally friendly. Since PLA is plant based, it is biodegradable and will break down over time, making it more suitable for the environment and for recycling. As another benefit, many users note a sweet smell during printing that is similar to baking, although I still wouldn’t recommend breathing in the fumes from PLA intentionally.

In general, both materials are great filaments to print with. I use ABS more it is because I tend to print a lot of structural parts, such as RC car suspension parts or parts that may see an elevated temperature. I have used PLA for more artistic prints, and for some electronics enclosures where the electronics don’t generate much heat.

Another filament that I didn’t mention has been gaining popularity; Polyethylene terephthalate glycol-modified (PETG) has the temperature range and strength similar to ABS, but without many of the difficulties associated with printing it. PETG also tends to be more expensive. I, personally, have not printed with it yet, although I do have some filament to experiment with in the future.