Filament Buying Guide

The filament you use is incredibly important. The wrong filament will result in failure. Unfortunately, there are tradeoffs between different filaments and there is no one best filament that you can choose. Here are some things to consider:

• Tensile strength. This is the basic unit of strength. Most testing is absolute tensile strength, the amount of stress required to fully break the sample. This is a good metric to use when comparing the strength of stiff materials, however, you need to consider other metrics as well.
• Youngs modules, or the elastic modules is a metric of stiffness. It’s a great way of comparing different filaments, stiffness is very important.
• Impact resistance is important, but can be hard to compare between filament manufactures as testing methods vary.
• Heat deflection temperature is another very important metric. This is basically a unit of temperature resistance. Different testing methods will give different results, so keep an eye on the amount pressure / force that was used in the test.
• Print temperature is also important, not from a durability standpoint, but from a printability standpoint. If you can’t print it, it won’t help you. So keep in mind the limits of your printer when you are looking for filaments.

How much strength is enough? Here are some starting points:

• Tensile strength of 7000 PSA (48 MPa) or greater.
• Young’s modulus of 350,000 PSI (2400 MPa) or greater.
• Try and compare impact testing data to other filaments from the same manufacture or testing house. You want to compare results that where measured consistency using the same methods.
• The higher the heat deflection temperature the better, other then the potential printing difficulty of higher temp filaments.

Just because a filament has all the right metrics and the data sheet checks out, does not mean it’s a good option. Keep an eye on what filaments others are using successfully, or unsuccessfully.

There is another metric that can be hard to nail down. Layer adhesion. Layer adhesion is dependent on many factors, but one of them is is the filament. Some filaments have better adhesion then others.

Here are some filament types and there pros and cons. If you are new to printing, start with PLA+. The Polymaker PLA Pro is the best.

PLA: This is the most common filament, and comes with a wide variety of properties. Standard PLA tends to be stiff, strong, and brittle. PLA+, Pro PLA, Performance PLA, and other “improved” PLA’s is what we normally use. They are weaker and more ductile then regular PLA, but have very good impact resistance, giving them great mechanical properties. PLA+ is a great option for your first prints. Don’t let it get hot, and it will serve you well. If PLA+ had good heat resistance, it would be the go to filament for most applications. Fiber filled PLA is not recommended.

ABS (or ASA): Often it is said that these filaments are stronger or “tougher” then PLA+. This is untrue. ABS has poor tensile strength and decent impact resistance. Layer adhesion tends to be poor without a heated chamber. ABS does have good temperature resistance, and that can make it a good option for some parts. For low stress long term parts ABS is probably one of the best options, as it does not suffer from creep or stress cracking. However, due to it’s low strength, it is not recommended for weapons components.

PETG: A popular filament often said to be “tougher” then PLA+. As with ABS, this is untrue. PETG has mediocre strength and very poor impact resistance. It’s a deceptive material, and can appear to be tough and ductile, but under sharp impact it can shatter. PETG does have better heat resistance then PLA+, but it’s not that great. PETG is very stable and does have very good chemical resistance, however its not good for parts subject to mechanical stress or impact. I do not recommend PETG at all. Don’t waste your time.

PC: Polycarbonate is a strange material. It’s strong and stiff, can have good impact resistance, but can also have poor impact resistance. It also has great temperature resistance. But it’s main flaw is something called constant stress cracking. This is where PC parts slowly develops cracks at stress levels below the excepted yield strength. Because of this it is not recommended. It also tends to warp, and is difficult to print larger parts.

PA: Nylons are a wide category. Unfilled Nylons will be discussed here. Nylon is a flexible material with great wear resistance and good temperature resistance. Most unfilled Nylons are too flexible for most weapons parts, but for more flexible tough parts it can be a good option. Nylon has two primary flaws, creep and water absorption. Creep is when the material yields under constant pressure at a strain level below the excepted yield strength. It can result in pins moving and parts bending over time. Annealing can reduce this issue to some degree. Water absorption is when the Nylon absorbs water from the air and becomes less stiff. This effect can drastically reduce the strength and stiffness of a part. Unfilled Nylons can also be hard to print. Due to these issues, unfilled Nylons are not recommended for most weapons parts. The only component which may benefit from this material is the SL-9 ejector, as the part is not subject to constant stress that would result in creep, and the high durability is beneficial.

FILLED PA: Nylons are the most common filament to add a fiber fill to. There are two main options, glass fiber and carbon fiber. The fibers do a few things to improve the properties of the filament. They increase strength and stiffness, reduce warping and curling, can improve the impact resistance, and can reduce the amount of creep. The downsides of fibers are more nozzle clogs, higher cost, rough surface finish, and possibly less layer adhesion.

CARBON VS. GLASS FIBER: Carbon fiber is stiffer and does a better job stabilizing the print to reduce curling and warping. Glass fiber is less stiff and will not prevent curling as well, but it does result in somewhat better impact resistance. In general carbon fiber is preferred.

The amount of fiber used is also an important factor. The higher the fiber content the more the effects are amplified. Too high and layer adhesion will suffer, and nozzle clogs will be common. A low fiber content will result in a easy to print material with a great surface finish, but it will still be quite flexible. Many carbon fiber Nylons fall into this category, so beware.

PA12 VS. PA6: This where we get more into the weeds on Nylons. PA6 absorbs more water then PA12, and will become less stiff afterwards. PA12 is not as strong to begin with, but will not lose as much strength. However, PA12 has very high creep, and even after annealing the creep levels are too high for some parts. There are blends, such as PA612, that may be a good compromise, but more testing is needed.

FILLED PET: This is a relatively new filament that has a number of attractive properties. Carbon fiber filled PET is stiff and strong, does not absorb water, and has low creep. The concern with PET is that it may suffer from impact resistance like PETG, however during testing this has yet to become an issue.

TPU: Thermoplastic polyurethane is a rubber that can be 3D printed. Due to being soft and flexible it is not used in the same ways as the other filaments on this page. It is good for ergonomic parts, or parts like the hose clamp cover. Due to it falling into a very deferent use category, pros and cons are not listed. Don’t use this filament unless it was specified by the designer.

There are other less common filaments, but they have not been mentioned to to a lack of suitability or a lack of information.

Now that you have a basic overview of the filament options available, here are some recommendations for specific filaments:

PLA: Polymaker PLA Pro. All around the best PLA+. Available in FDE as well 😉

CARBON FIBER NYLON: Polymaker PA6-CF. This material may still be a bit too flexible in high humidity, but it’s a solid option.

GLASS FIBER NYLON: COEX Glass Fiber Nylon. This is a solid filament, the very high fiber content maintains it’s stiffness in high humidity, however it does have a rough surface finish and is prone to nozzle clogs.

CARBON FIBER PET: Bambu PET-CF. This is the best filled PET I’ve tried.

TPU: Ninjatek Ninjaflex. Great TPU filament.