The original fused deposition printers almost exclusively used ABS (acrylonitrile butadiene styrene) as their substrate for printing. ABS has nearly ideal properties for rapid prototyping in plastic: it’s a strong, slightly flexible plastic that extrudes cleanly at between 220° and 240° Celsius. ABS is used in Lego bricks and is one of the most commonly used industrial and commercial plastics.

For FDM printing, ABS requires a heated print bed to ease the thermal shock. Heating the print build plate helps the plastic adhere to the plate for stability and prevents it cooling too quickly, which could lead to thermal deformation (a sort of curling or separation when ABS cools rapidly after being extruded). ABS is sensitive enough in this arena that many people who print ABS learned early on that enclosing the printer would increase the stability of prints because it regulated the temperature around the printer. I discovered early in my printing experiments with an early MakerBot printer (Replicator 1) that even a strong breeze blowing in the wrong place (i.e., across the print bed) could wreak havoc with getting a good print out of the printer. Higher-end printers will have an enclosed print area built in, while less expensive ones won’t.

One of the advantages of ABS is that it dissolves in acetone. Acetone dissolves ABS completely, but used sparingly it can act as a glue to fuse two ABS printed pieces together permanently. Acetone is also used to make a “glue” for print beds to make them sticky for the initial printed layers. Acetone vapor is heavier than air, and some people have used this property to build acetone vapor baths that act to smooth the edges of layers of an FDM ABS print.

ABS has caught some bad press recently as the potential effects of off-gassing of the heated plastic and microparticulate effects are studied. As a petroleum-based plastic, ABS does produce a distinctive stink when printing. Fumes have been reported to cause headaches, and some studies link ABS fumes to olfactory loss.¹ One study found ABS printing releases high volumes of ultrafine particles that could be dangerous when inhaled.² These are preliminary studies. Most haven’t been repeated, and the science is still rough on the health effects. But if you need to print with ABS, it may be a good idea to take venting into account.

PLA (polylactic acid) is the second-most popular printing substrate for FDM printers. PLA is a bioplastic, made from corn, beets, or potatoes, and is compostable in commercial compost facilities (the heat and bacterial action in home composting aren’t high enough to break it down). It melts at a much lower temperature than ABS (150–160°C), but it is typically extruded at a higher temperature, anywhere from 180°C to 220°C depending on the PLA itself. Because of its lower temperature, it’s not suitable for uses that involve high temperatures and direct sunlight. PLA is also very different from ABS in term of fragility; PLA is far more crystalline and shatters or cracks more readily than ABS, rather than deforming under pressure.

However, MakerBot and other major manufacturers are now starting to go with PLA as their primary printing plastic. PLA doesn’t require a heated bed to promote adhesion or prevent thermal curling, which lowers the price of the printers that use it. It’s far more thermally stable during printing than ABS as well, and much less likely to warp or curl due to errant breezes. It is possible to reliably print PLA without needing to enclose your printer, which can be a huge benefit in many circumstances.

The other significant advantage is that PLA is far more pleasant when printing than ABS. Because it is a bioplastic, when heated it smells like waffles or syrup and not like an oil spill. It also hasn’t been linked to any type of medical issues from being heated, although the study of all these plastics is young when it comes to 3-D printing specifically.

One of the other advantages of PLA is that it’s available in dozens and dozens of colors, including both opaque and partially transparent, as well as a couple of glow-in-the-dark colors. It also is available in a flexible form, which can produce prints that are almost rubber-like in consistency.

If you are printing in a library setting, I would suggest concentrating on using PLA. Between reliability and ease of working with it, it’s a far better choice than ABS for printing in a public space.

Once you get beyond ABS and PLA, you’re in the realm of specialized plastics that are used for specific properties rather than for general 3-D printing. There are more and more of these practically every day, but generally they fall into a couple of categories: dissolvable support material, specific required material qualities, or nonplastic powder suspended in a thermoplastic resin. I’ll describe the most common of these below.