ABS vs ASA outdoors: why one turns yellow in the sun

Some prints live outside, in sun, rain and heat. So today: ABS and ASA, two plastics made for tougher jobs. And why only one of them likes the sun.

You print a part for the garden in ABS, because it handles heat. A summer or two later, it's yellow and chalky, and it snaps at the first knock. And the reprint? Its corners curl up off the bed.

Here's this episode's model: a plant stake with a label. Print one in each plastic, stick them in the garden, and let the sun run the test. Round corners help against warping. And the groove down the middle is your tape line. About 8 grams each.

A rib along the stake keeps it stiff when you push it into hard soil. And the long point helps it slide in. It lies flat, so no supports.

First, heat. In Material Match number one, PLA softened around 60 degrees and PETG around 80. ABS and ASA both soften around 100. That's why they're popular for parts in a hot car or close to a motor.

Now, pause and guess. Heat isn't their weak spot. So what turns ABS yellow and brittle outside? A: the heat. B: sunlight. Or C: rain?

It's B: sunlight. Ultraviolet light, to be exact. The heat was never the problem for ABS. The sun is.

Here's why. Both are a hard, glassy plastic with tiny rubber beads mixed in. Those beads make it tough. In ABS, that rubber is butadiene, and UV light slowly breaks it down. The surface yellows, goes chalky, and the part loses its toughness.

ASA swaps that rubber for an acrylic one, which handles UV far better. About as tough, about as heat-proof, but it lasts outdoors. That's why ASA shows up in car mirror housings.

Now the catch: ABS and ASA warp. Each new layer goes down hot, then shrinks as it cools. It pulls on the cooler layers below, and the corners curl up off the bed.

And they have further to go. ABS and ASA go stiff around 100 degrees, PLA around 60. Cool down to a 20 degree room, and that's 80 degrees of cooling instead of 40. Twice as far. A warm enclosure at about 40 degrees cuts that by a quarter, and it keeps out drafts.

In your slicer, start from the ABS or ASA profile, and check the range on the spool. Everything runs hotter. In this example, the nozzle goes from 215 to 250 degrees.

And the bed from 60 to 100, to keep the first layers warm.

Then turn the part cooling fan way down, so the layers cool slowly and bond well.

And add a brim, so the corners have something to hold on to. A clean plate and a good first layer matter double here. Start Here number one shows you how.

While printing, ABS and ASA give off more fumes than PLA, styrene among them. So ventilate the room, use an enclosure with a filter if you can, and don't print where you sleep.

So, which one? Both handle heat. Both are tough. Both want warm, still air. But for anything that lives in the sun, pick ASA. ABS is fine for hot parts out of the sun, like an electronics box.

In short: ABS and ASA both soften around 100 degrees. In the sun, pick ASA, not ABS. And give them warm, still air, so they don't warp.

The plant stake is free to download. Tape off half of each label, and leave them in the sun all summer. Tell me in the comments: what's the first thing you'd print for outside? Next time: TPU, the plastic that bends and bounces back. Subscribe so you catch it. I'm Spoolbert, see you in the next one.