How to Choose the Right Filament

After you pick a 3D printer, the first decision you'll have to make is what type of filament you want to use. There are several dozen varieties—even setting aside the numerous colors they come in. Wading through them surfaces a string of chemical-sounding names: polylactic acid, polyvinyl alcohol, carbon fiber, and the tongue-twisty thermoplastic elastomers, for example. They go by a dizzying variety of acronyms, ABS, PLA, HIPS, CPE, PET, PETT, TPE, PVA, and PCTPE among them. But don't be dismayed by this alphabet soup. Only a few types are in common use, and manufacturers tend to eschew overly geeky monikers in favor of more descriptive names alluding to an essential quality of the filament such as flexibility (NinjaTek's Ninjaflex and Polymaker's Polyflex, for instance) and strength (Makerbot and XYZprinting both market filaments called Tough PLA, and Ultimaker will soon introduce a tough PLA of its own).

Filament Basics

Filaments used in 3D printing are thermoplastics, which are plastics (aka polymers) that melt rather than burn when heated, can be shaped and molded, and solidify when cooled. The filament is fed into a heating chamber in the printer's extruder assembly, where it is heated to its melting point and then extruded (squirted) through a metal nozzle as the extruder assembly moves, tracing a path programmed into a 3D object file to create, layer by layer, the printed object. Although most 3D printers have a single extruder, there are some dual-extruder models that can print an object in different colors or with different filament types.

The process of printing with plastic filament is called either fused filament fabrication (FFF) or fused deposition modeling (FDM). They're the same thing; the FDM acronym is trademarked by 3D printing pioneer Stratasys Corp., so other manufacturers created their own names to describe their printers' technology; FFF is the one that caught on. Even today, except in some manufacturers' brochures, you'll see the names used interchangeably.

Filament is sold in spools by weight ranging from 0.5 kilogram to 2 kilograms. The filament comes in two thicknesses, 1.75 millimeters and 3 millimeters. (The latter is in reality a little thinner, about 2.85 millimeters.) The vast majority of filament is of the 1.75-millimeter type; Ultimaker and LulzBot are among the few manufacturers whose printers use the thicker size. Weight is almost always listed in metric units.

Now, let's take a look at a few of the more popular and important filament types.

The Dynamic Duo: ABS and PLA

By far, the most common filament types are acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA). Most basic 3D printers are designed to exclusively use these filaments. Part of their appeal is that they're relatively inexpensive, costing as little as $20 per kilogram.

Don't be put off by ABS's unwieldy chemical name; it's the same plastic used in Legos. Objects printed from ABS are tough, durable, and nontoxic. It has a relatively high melting point, with a print temperature ranging from 210 degrees to 250 degrees Celsius. The bottom corners of objects being printed with ABS have a tendency to curl upward a bit, especially if you are using a non-heated print bed. During printing, ABS can emit an acrid, unpleasant odor, so it's best used with a closed-frame printer in a well-ventilated room.

PLA has a relatively low melting point, with usable temperatures between 180 degrees and 230 degrees Celsius. It is plant-based and biodegradable. It's harder than ABS, prints without warping, and is generally easy to work with, although in rare cases it can cause extruder jams. PLA is often used as the base material for more exotic, composite materials, which we will discuss in a bit.

Nylon

Nylon is an incredibly versatile synthetic material, developed in the 1930s, that has found use in everything from toothbrushes to parachutes to tires to stockings, and now 3D printer filament. At its heart it's a polymer, or plastic (or, more precisely, a family of plastics). It is strong and durable, yet flexible, and among the lowest-priced 3D printing filaments. It melts at a higher temperature (about 240 degrees Celsius) than most filaments. Not all 3D printers are built to handle that heat—some commonly used substances in the extruder emit fumes at that temperature. Like with ABS, objects printed with nylon have a tendency to warp, which can be mitigated by using a heated print bed.

Flexible Filament

TPEs (or thermoplastic elastomers) are thermoplastics with high elasticity (though still far short of, say, rubber bands); objects printed with them are relatively flexible. One common TPE type is thermoplastic polyurethane (TPU), of which NinjaFlex is a popular example.

Soluble Filaments: HIPS and PVA

One of the more catchy acronyms, HIPS, stands for high-impact polystyrene. HIPS is moderately priced, lightweight, and can be sanded, glued, and colored with acrylic paints. It is similar to ABS, except that HIPS is soluble in Limonene, a citrus-based solvent, making it a good choice—when printing with a second material (such as ABS or PLA) with a dual-extruder printer—as a support material that could be dissolved after printing. It also prints well on its own, and is the filament recommended by LulzBot for its LulzBot Mini 3D Printer, which earned our Editors' Choice. MakerBot Dissolvable Filament is also comprised of HIPS.

Another soluble filament is PVA (polyvinyl alcohol), which conveniently dissolves in water. PVA is odorless, nontoxic, and biodegradable. It has a low melting point, and can jam an extruder nozzle when overheated. It is often used as a support material in dual-extruder printers; I tested the Ultimaker 3 by printing a test object—a box within a box—using PLA for the boxes themselves and PVA as the support. After the object was printed, I immersed it in warm water, and the PLA gradually dissolved, leaving the pair of nested boxes.

Composite Filaments

Composite filaments have a base of PLA or other thermoplastic into which particles, powders, or flakes of other materials have been mixed. Some are wood blends, others include sandstone or limestone, and still others have various kinds of metals, including iron, aluminum, brass, bronze, and copper. These filaments take on some of the properties of the materials they have been mixed with. Another popular composite is carbon fiber; objects printed from it take some of the strength of the fiber. A downside to these composite filaments is that they cost considerably more than non-composites.

Beyond Plastic Filament: Resin-Based Printing

With today's proliferation of FFF printers, it's easy to overlook the fact that there are models on the market based on other technologies that don't use filament. Chief among them is stereolithography (aka SLA), the first 3D printing technology to have been developed, and which is capable of very detailed, high-resolution prints. Price tags for SLA printers for commercial use can run well into five (and even into six) figures, but we have seen some lower-priced models, suitable for hobbyists and artisans.

In SLA printing, an ultraviolet laser traces the shape of the object to be printed, layer by layer, on a UV-sensitive resin (aka photopolymer, or photopolymer resin) housed in a tray or vat, and the resin exposed to the laser hardens to form the printed object. The resins come in 500-milliliter and 1-liter bottles, with prices from printer manufacturers starting at about $100 per liter. Some manufacturers have formulated resins for strength, flexibility, rigidity, and other qualities, and such resins tend to sell at a premium. Resins have suffered from a limited color palette, and have tended to be confined to black, gray, white, and clear, though some brighter-colored and metallic resins have become available of late.

DLP is a form of stereolithography that uses a projector in place of the laser as a light source, using visible light instead of ultraviolet. The projector, which employs Texas Instruments' DLP (Digital Light Processing) technology, projects a series of images into a vat of photopolymer resin similar to the resins used in SLA printing to build the object, layer by layer.

Now that you know everything you need to about the most popular filaments, you'll want to read our 3D printer buying guide, which includes reviews of the best models we've recently tested. You can also check out what an early adopter had to say about his time learning to print in 3D.