Things you should know about flexible filaments and Nylon

Ok, let’s talk about Nylons, or Polyamides and flexible 3D printing materials. They’ve been around for a while, but I still think they are a super interesting – even if I wouldn’t print everything with them.


So why am I pairing up Nylons and flexibles into one video? Well, because they’re both soft and many of the same rules apply to both of them. Let’s start with Nylons or PAs – there are a few different types that actually behave quite differently. First off, there are a few different Nylon base types that will be used for 3D printing, and those are PA6, PA6.6 and PA12. PA 6 is the softest one and the one that absorbs moisture the fastest – some PA6-based filaments will become unprintable within hours if left out in the open. PA6.6 is a bit less sensitive there and PA12 is generally the least moisture sensitive. When printing, you want the filament to be as dry as possible, so whatever Nylon type you print, definitely keep it in a drybox and print out of the drybox, don’t take it out when you load it onto your printer. Even PA12. The usual tip with baking filament in the oven still applies here, and if you don’t have a drybox and only plan on doing short prints, you may even get away with just baking your Nylon filament right before every print.

Now, what you have to keep in mind is that not only your raw filament can absorb moisture, but also your finished printed parts. This plays a big role in how tough a Nylon print ends up being and it can make a huge difference in how rigid your part ends up – some of the Nylon prints off the Markforged machine went from “raw spaghetti” to “perfectly al dente” within two weeks after being printed, and that, in either case, needs to be considered the “final” form of your Nylon prints.

There are also some Nylon copolymers or blends available that mix some of the properties of other materials with the toughness of Nylon.

Yes, toughness, that’s actually something that Nylons share with flexibles. As I’ve mentioned in the “introduction” video of this series, flexible materials can recruit more material of their cross-section to take care of point loads, so they will feel basically indestructible. And if you actually measure how the parts perform, it’s the same story. This stuff is incredibly tough.



Alright, we still need to talk about flexibles. And here as well, there are a few different types – some the earliest ones were modified, softened PLA, but nowadays most filaments are TPU or Thermoplastic PolyUrethane. You might also hear TPE thrown around, but that’s just a generic “ThermoPlastic Elastomer” abbreviation and could be anything. Flexibles come in a wide range of softnesses, from “OMG how are you supposed to print this” to “Well, I could have just bought ABS”. The most common one is Shore hardness 95 on the A-scale, which is a relatively hard grade. The nice thing about that is that, depending on how much infill and what wall thickness you use, parts can come out mostly rigid, or with a healthy amount of flex. It’s also comparatively easy to print. Both with the softer Nylons and the softer TPU flexibles, your 3D printer will need an extruder that is extremely well-constrained, so everything after the drive gears needs to be seamless, without gaps, really smooth and low-friction. Flexibles is actually one of the use cases where a bowden-lined hotend makes the most sense, even vs an all-metal one. Warm flexible filament gets extremely tacky and the Teflon can help it run with reduced friction through against the walls. Though if your hotend, extruder path or even your bowden tube are too wide for your filament, then flexibles will buckle either way, which is not great for friction or reliability at all.

So how you print these materials? Slowly. Methodically. Sensually.

Take your time. Go slow. You have nothing to lose by having a flex print take a bit longer, but you’re dramatically increasing your chances of the print coming out the way you wanted. Now, granted, extremely soft filaments are tough to print either way and steeper overhangs are going to curl because the softer material can’t counteract the forces of a cooling and contracting fresh layer. But if you have a medium-hardness material or the more rigid Nylons, then you can get some really nice quality out of it. For print settings, you should keep in mind that not only are your printed parts flexible, but also the filament going into your hotend. Meaning as your extruder tries to push filament into the hotend, it’s actually only going to compress the filament instantaneously and then that pressure will slowly get released through the hotend. Now that means two things: First of all, retracts are not going to work all too well, so you could increase the retract length by a ton, but that’s going to chew through your filament in no time, so the best thing to do is to turn off retracts completely or stick to parts that don’t need retracts in the first place. It also means that speed changes during a print won’t work all too well, so a more consistent speed instead of “highly optimized” speeds for infill, shells etc is a good option. Of course, this all depends on how rigid your filament is, some of the harder materials are much less picky about these things.


Bed adhesion

Now, so far Nylons and Flexibles all play by somewhat similar rules, but when it comes to bed adhesion, they’re quite different: Nylons are hard to stick down, while TPUs will stick and often permanently bond to a ton of surfaces. So let’s start with Nylons – the old wisdom was to use phenolic paper for Nylons, but many of the PVA-based bed adhesives work great as well and are easier to use. That ranges from glue stick over diluted wood glue over to specialized bed adhesives – as long as they contain PVA somewhere, and most of them do, chances are that they will have Nylons sticking well. Now, flexibles and especially TPUs tend to stick too well. Avoid PEI at all costs and always put a layer of, well any of the adhesives that work for Nylon over it, but the good thing is that many flexibles will also very easily stick to low-temperature beds or even unheated surfaces like plain, clean glass, simply because they don’t have any rigidity to actually pull themselves up.

So the nice thing about TPU is that it’s super easy to attach to other parts – superglue etc work extremely well, and if you dual-extrude TPU with PLA or ABS, it will bond nicely. Nylon, on the other hand, is the exact opposite. Just forget about gluing it, and use screws and threads instead.

So, where would you use these materials? Nylon, because it is typically a bit flexible, but also very slippery, is a great material to use wherever the printed part needs to mate with something else, be it for fixtures or phone mounts or super-durable cases. The more rigid Nylon types and the fiber-filled ones are a great option for many of the pars ABS or PETG would typically be used for if you need that different set of properties. Flexibles, on the other hand, can make great seals, hinges, lids, vibration dampers, soft feet for things, RC car tires, chewie dog toys etc, but keep in mind that anything that is 3D printed will have a ton more nooks and crannies where crap can get stuck in, so keep any dog toys clean, but 3D printed parts are also not super-duper temperature resistant. So yes, print seals for maybe a 3D printed electronics case, but not necessarily a new head gasket for your car.

Alright, so that should cover the two rather flexible options for 3D printing filament. Do you have any other tips on how to print these? Then leave a comment below or post them in the community forum! If you learned something, hit that thumbs up, get subscribed for more and if you want to support this channel directly, Patreon is one option, but so is just buying things through the affiliate links in the video description, for example from Amazon or from today sponsor, Aprintapro. As always, thank you for watching, and I’ll see you in the next one!

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