Nylon (PA): bubbles, stringing and weak layers from moisture, or parts that warp

Symptom

When printing nylon, bubbles and popping come out of the nozzle, the surface is uneven and stringy, parts are weaker than expected, or they warp and come off the plate.

Likely causes, from most to least likely

1. Moisture: nylon is very hygroscopic; stored badly it can absorb water up to 10% of its weight, according to Prusa.
2. Insufficient drying or filament left in the open while printing: in a normal room it picks up moisture again within hours.
3. Crystallisation shrinkage on cooling: nylon warps if the chamber is cold or the plate is not prepared.
4. Unsuitable surface: Prusa recommends a dedicated nylon sheet; Bambu Lab requires glue.
5. Insufficient temperature: Prusa prints its nylon at 285 °C with the bed at 110 °C.

Checks to tell which one it is

• Purge a little: bubbles or popping mean it is damp.
• Think about how long the spool has been open and how it was stored; a thermo-hygrometer in the box tells you the real humidity.
• Check whether you print enclosed and away from draughts.

Before you start

Before taking anything apart, cleaning or adjusting it, switch the printer off and unplug it, unless a step says otherwise, and do not touch the nozzle, the heater block or the bed until they have cooled down. If in any doubt about electricity, heat or moving parts, stop and ask a professional.

Step-by-step fix

1. Dry before printing

   Dry nylon before printing: Prusa says at least 4 h below 90 °C, and Creality 80-90 °C for 8-12 h for PA and PA-CF. For nylon and other very hygroscopic materials, Prusa recommends always storing them dry or drying them before every print.

   Check: No more bubbles when purging and the surface improves.

   If that does not fix it: Print from a dry box (next step).

2. Print from a dry box

   Print with the spool inside a dry box or an enclosed system with effective desiccant. Bambu Lab advises keeping humidity below 20% and monitoring it with a thermo-hygrometer, especially with PA and PA-CF.

   Check: Quality is the same at the start and the end of the spool.

   If that does not fix it: Deal with warping (next step).

3. Prevent warping

   Print with an enclosure or heated chamber. Clean the plate and apply glue (or use the nylon sheet) and add a brim. Avoid infill above 50% and more than 6 walls (Bambu Lab). Carbon fibre versions warp much less.

   Check: The part does not lift off the plate.

   If that does not fix it: Raise the bed temperature slightly within the maker's range.

4. Ventilate and use the right nozzle

   Nylon gives off a strong smell and ultrafine particles: print in a well-ventilated room or enclosed (Prusa). If it is fibre-filled nylon (PA-CF), use a hardened steel nozzle.

   Check: No smell builds up and the nozzle does not wear.

   If that does not fix it: Consider another material for that part.

Prevention

• Always store nylon sealed with desiccant, never in the open.
• Dry it before each use if you do not keep it stored dry.
• Print it enclosed with the room ventilated.

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Printers it applies to

Any FDM (filament) 3D printer, from any brand.

Material: PA.

Official sources

This guide summarises the official documentation linked here:

• Polyamide (Nylon) (material guide) · Prusa Research
• Drying filament · Prusa Research
• Filament Pre-Printing Guide: Drying · Creality
• Sealed Box (humidity requirements) · Bambu Lab
• ASA CF / PAHT CF Usage Guide · Bambu Lab