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I'm working on a project with will be buried in soil. It's an enclosure for a sensor that will be potted inside the 3D printed part. What filament will give me the longest life in soil?

ETA: burial will be permanent, and I'd like it to last at least five years.

ETA: The printed part will provide mechanical support for the sensor, so it needs to retain most of its mechanical properties.

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  • $\begingroup$ How long are you keeping it buried? $\endgroup$
    – 0scar ♦
    Commented May 2, 2020 at 22:00
  • $\begingroup$ Do you need the part to protect the sensor or anything else inside? Or just to retain its own form? $\endgroup$
    – R.. GitHub STOP HELPING ICE
    Commented May 2, 2020 at 22:17
  • $\begingroup$ My guess would be TPU. If I find supporting evidence I'll post an answer. $\endgroup$
    – R.. GitHub STOP HELPING ICE
    Commented May 7, 2020 at 6:00

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I would recommend PETG - only because it is structurally similar to the plastic used in the bottles that last forever, and most PETG is food grade - implying that its chemical stability should be reasonably good...

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  • $\begingroup$ I feel the same about PETG. If you want something at normal cost, that's the way to go. There are also polycarbonate filaments, that are said to be more resilient than anything, but are difficult to print and come at a higher cost. $\endgroup$
    – IsawU
    Commented Jun 13, 2020 at 9:24
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If TPU ends up not being rigid enough for you: I've had good enough luck with ABS coated in automotive RTV.

Thing with ABS though is that it's a special (not so)"solid" that gets softer as it gets hotter. My use had water in it when warm so wasn't too much of an issue, and it never experienced freezing temperatures.

Also it hasn't been 5 years yet. ~2 years and counting.

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Instead of TPU or ABS, you might also want to try ASA. It has a better resistance against weather, so it might help you here.

Here is a little article about ASA filament: Article

And this article lists its pros as having a strong UV resistance, high wear and impact resistance, and high glass transition temperature.

Overall, you might want to give this a try. Hope it helps!

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  • $\begingroup$ ASA is said to be hygroscopic - able to capture and contain air humidity. Given the humidity in soil, I'd be skeptical about this one for this application. $\endgroup$
    – IsawU
    Commented Jun 13, 2020 at 9:19

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