Nylon is the heartbreaker of the 3D printing world. You buy a spool of PA6 or PA12 because you need that incredible tensile strength and chemical resistance for a functional part, maybe a gear or a custom bracket. It looks beautiful coming out of the vacuum-sealed bag. You start the print, and for the first hour, everything is golden. Then, the popping starts. It sounds like tiny firecrackers going off inside your hotend. By hour four, your part looks like toasted Swiss cheese, covered in stringing and structural voids. Honestly, it’s frustrating. The culprit isn’t your retraction settings or your leveling; it’s the fact that you aren't using a high-temp filament dryer for nylon.
Nylon is aggressively hygroscopic. That’s just a fancy way of saying it drinks water right out of the air like a sponge in a monsoon. Even in a "dry" room with 30% humidity, a fresh spool of nylon can become unprintable in less than six hours. When that moisture-laden plastic hits a 260°C nozzle, the water turns into steam instantly. This creates bubbles, destroys layer adhesion, and ruins the dimensional accuracy you need for engineering-grade parts.
The Brutal Reality of Drying Nylon
Standard PLA dryers usually top out at 50°C or 55°C. If you try to use one of those for your PA6-CF or bridge nylon, you’re basically wasting electricity. It won’t work. To actually migrate moisture out of the polymer chain of nylon, you need heat—and a lot of it. We are talking 70°C to 85°C for 12 to 24 hours. Most hobbyist-grade "dryer boxes" are just glorified food dehydrators that can't reach these sustained temperatures.
If you don't hit the glass transition temperature ($T_g$) or get close enough to encourage molecular movement, the water stays trapped. You might dry the outer millimeter of the filament, but the core remains soaked. This leads to "false hope" prints where the first few layers are okay, but the quality falls off a cliff as the printer pulls from deeper within the spool.
Why your oven is a terrible idea
I’ve seen people try to use their kitchen ovens. Please, don't. Most residential ovens have massive temperature swings. You set it to 170°F (about 77°C), but the heating element blasts it to 210°F to get there, and suddenly you have a $60 puddle of melted plastic fused to a plastic spool. It’s a mess. Plus, industrial plastics like nylon can off-gas. You really don't want those fumes lingering where you bake your pizza.
Choosing a Filament Dryer for Nylon That Actually Works
When you’re shopping for a filament dryer for nylon, you have to look at the specs beyond the marketing fluff. You need an active heating element and, more importantly, a fan for air circulation. Without a fan, the bottom of the spool stays cold while the top gets scorched.
- Temperature Range: Look for a unit that specifically lists a maximum of at least 70°C. Units like the Eibos Cyclopes or the Sunlu S4 are popular because they actually hit the numbers required for engineering materials.
- Desiccant vs. Active Heat: Don't rely on "dry boxes" filled with silica gel for the initial drying phase. Silica is great for keeping filament dry, but it’s nowhere near powerful enough to pull moisture out of saturated nylon.
- Feed Holes: Since nylon re-absorbs moisture so fast, the dryer needs to act as a dry box during the print. Ensure the unit has a PTFE tube outlet so the filament goes straight from the heated chamber into your extruder without touching the ambient air.
The Science of Evaporation
It’s not just about heat; it’s about relative humidity (RH) inside the box. As the air inside the dryer heats up, its capacity to hold moisture increases. If that moist air stays trapped in the box, the drying process stops because the air becomes saturated. This is why high-end dryers or modified food dehydrators work better; they often have a slight vent or a way to cycle the air. If your dryer is sealed tight, try cracking the lid a millimeter or two. It sounds counterintuitive, but letting that wet air out is the only way to get the filament truly bone-dry.
Real-World Performance: PA6 vs. PA12
Not all nylons are created equal. PA12 (Polyamide 12) is slightly less thirsty than PA6. If you're using something like Prusament PA11 Carbon Fiber or MatterHackers NylonX, you'll notice they handle moisture a bit better due to the carbon fiber filler and the base polymer. However, "better" is relative. They still require a dedicated filament dryer for nylon to achieve that smooth, matte finish.
- PA6 (Polyamide 6): This stuff is a nightmare. It can absorb up to 10% of its weight in water. If you leave it out overnight, it’s done. You’ll need a solid 12 hours at 80°C to bring it back to life.
- PA12 (Polyamide 12): More dimensionally stable and absorbs less water. You can usually get away with 6-8 hours of drying, but you should still print it directly from the heated box.
Pro Tip: You can tell if your nylon is wet without even printing. Extrude some into the air. If it comes out clear and smooth, you're okay. If it’s cloudy, has visible bubbles, or makes a "hissing" sound, stop immediately. You're just wearing out your nozzle with steam-induced cavitation.
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Professional Setups and Modifications
For those who print nylon professionally, "prosumer" dryers often feel a bit flimsy. I know guys who use laboratory-grade vacuum ovens. A vacuum oven lowers the boiling point of water, allowing you to dry the filament at lower temperatures without risking the structural integrity of the plastic spool. But, those cost thousands.
For the rest of us, the best bang for your buck is often a modified circular food dehydrator. You can find these at thrift stores for ten bucks. You just snip out the plastic trays to create a vertical chamber. These things are built to run for 48 hours straight and move a massive amount of air. Just make sure to check the temp with an external thermometer, as the dials on cheap dehydrators are notoriously inaccurate.
Humidity Sensors are Liars
Most dryers have a built-in RH (Relative Humidity) sensor. Take those numbers with a grain of salt. When the air is 70°C, the RH might read 10%, but that doesn't mean the filament is dry yet. It just means the air currently in the box is dry. The moisture inside the plastic takes time to migrate to the surface. It’s a slow, diffusive process. Don't trust the screen; trust the clock.
Actionable Steps for Perfect Nylon Prints
If you want to stop failing and start succeeding with nylon, follow this workflow. It’s tedious, but it’s the only way to guarantee industrial-grade results.
- Dry before you fly: Put your new spool in a filament dryer for nylon at 75°C for a minimum of 12 hours before the first print. Yes, even if it came "vacuum sealed." Most factories use water baths to cool filament during extrusion, and that moisture gets trapped inside before it’s even bagged.
- The Weight Test: Use a precision kitchen scale to weigh your spool before and after drying. If the weight drops by 2 or 3 grams, that was all water weight. Once the weight stops dropping, the filament is dry.
- Print from the Box: Use a PTFE tube to guide the filament from the dryer directly to your printer's intake. Even a 20cm stretch of exposed nylon can start absorbing moisture during a 24-hour print.
- Store in Mylar: When the print is done, don't just throw the spool back in a Ziploc bag. Use heavy-duty Mylar bags with a fresh 50g packet of molecular sieve desiccant. Molecular sieves are far more effective than standard silica gel for low-humidity storage of technical polymers.
- Renew your Desiccant: If your silica gel has turned pink or clear, it’s useless. Recharge it in your dryer or a dedicated oven before trusting it with your expensive nylon.
Nylon is a powerhouse material that bridges the gap between hobbyist toys and real engineering. But without a dedicated drying strategy, it’s just an expensive way to clog your nozzle and give yourself a headache. Get the heat up, keep the air moving, and never print nylon "naked" in the open air.