We wouldn’t recommend most of our 3D printing materials for outdoor usage but it strongly depends on how you define outdoor usage. For instance, if you are using 3D printed parts for something like a longboard, materials like polyamide, alumide, and ABS are perfectly suitable. However, putting a 3D-printed birdhouse in your garden is a totally different story.
When a 3D-printed part is outdoors all the time, it will have to withstand all possible (extreme) weather conditions. Let’s use polyamide as an example. Since the material has a porous structure, it will get dirty and easily absorb moisture. If the temperature then falls below freezing point, we can’t predict what will happen because this has never been tested. Another and completely different weather condition is heat. Most materials are heat sensitive so being exposed to direct sunlight over a long time could deform your 3D-printed part.
The only materials that can be called weatherproof are high-detail stainless steel, aluminum, and titanium. Unfortunately, these corrosion-resistant metals don’t typically call for outdoor usage.