A viewer under My Tech Fun’s test of JLCPCB’s MJF PA12 asked whether he’d repeat the test with humidity-aged nylon. His reasoning: nylon “gets a lot of its toughness from some moisture absorption.” The channel replied that PA12 stabilizes after absorbing moisture for 10–14 days, which is about how long the parts took to arrive. PA12 also isn’t as moisture sensitive as PA6 or PA66. It’s a good exchange, and it shows why testing MJF parts needs a defined starting condition.
Should you condition parts before testing MJF parts?
Yes, if you want numbers you can compare. HP’s datasheet for HP 3D High Reusability PA 12 states how its own values were made: conditioning per ASTM D618 Procedure A, with testing done 48 hours after printing and unpacking, at 23 °C and 50% RH. Without that, you’re comparing your bars against HP’s in a different state.
Is the viewer right that moisture changes things?
Directionally, and the reply put it in proportion. PA12 doesn’t take up much water. Formlabs’ Nylon 12 datasheet lists water absorption of 0.66% by ASTM D570. The 10–14 day stabilization figure came from the video’s author, not from HP, so treat it as one tester’s experience. HP’s datasheet doesn’t give a figure for how long PA12 takes to stabilize.
What matters for a shop is consistency. A bar broken the day it comes out of the build unit and a bar that sat in a humid shipping box for two weeks aren’t the same test.
Does this matter for production parts?
For first-article checks, yes. If a customer measures a snap-fit or a hinge on a dry part straight from your bench, and you measured yours after a week on the shelf, you can both be right and still disagree.
How do you set up a fair test?
Copy HP’s recipe. Hold the parts at 23 °C and 50% RH for 48 hours after unpacking, then test. Write the conditioning time and room conditions on the test report. If the part will live somewhere wetter or drier, run a second set conditioned that way and report both.
Related on the Solvi blog: MJF Humidity: How Room Conditions Affect Your Builds; PA11 vs PA12 on MJF: When Is PA11 Worth Running?; MJF Threads: Print Them, Tap Them, or Use Inserts?.
Sources: YouTube: SLA vs MJF (PA12-HP) from JLCPCB, My Tech Fun, viewer question and reply; HP 3D High Reusability PA 12 datasheet (PDF); Formlabs Nylon 12 Powder technical data sheet.