Annealing means heating a finished 3D print to a controlled temperature, holding it there, then letting it cool slowly. Done right, it can make PLA parts noticeably more heat resistant and stiffer. Done wrong, it shrinks and warps them. Here's how to anneal PLA and PETG prints, what to expect, and how to avoid ruined parts.
What Does Annealing Do to a 3D Print?
When filament leaves the nozzle, it cools quickly and freezes in a mostly disordered state. Annealing warms the part enough for the plastic molecules to rearrange.
- PLA is semi-crystalline, so annealing lets it form crystals. That's where the big gains come from: higher heat resistance and more stiffness. The trade-off is shrinkage and possible warping.
- PETG and PCTG are amorphous, so they don't crystallize. Annealing mainly relieves internal stress and can slightly improve layer bonding. The gains are much smaller than with PLA.
Pros and Cons of Annealing
| Pros | Cons |
|---|---|
| Higher heat resistance (especially PLA) | Parts shrink, usually in X and Y |
| Stiffer, more rigid parts | Parts can grow slightly in Z (height) |
| Less internal stress | Thin or tall parts can warp or sag |
| Uses an oven you already have | Results vary by part shape and filament, so test first |
How to Anneal PLA
- Print with annealing in mind. Use more walls and higher infill. Solid, chunky parts handle annealing far better than thin-walled ones.
- Check your oven's real temperature. Use a separate oven thermometer. Many ovens run 10–20°C off at low settings, and overshooting will melt or slump the part.
- Preheat to a typical annealing temperature of 70–90°C. That's above PLA's glass transition (about 55–60°C) but well below its melting point. Start low, around 70–80°C, for your first tests.
- Support the part. Set it on a flat tray lined with parchment paper. For parts that must keep their shape, pack them in fine salt, sand or plaster powder so they can't sag.
- Bake for 30–60 minutes. Bigger, thicker parts need the longer end.
- Turn off the oven and let the part cool inside it. Slow cooling reduces warping. Don't pull it out hot.
How much does PLA shrink when annealed?
It varies with the part, the filament and your temperature. Shrinking a few percent in X and Y is common, often with a small increase in height. If dimensions matter, print a test piece, anneal it, measure it, and scale your model in the slicer to compensate.
Does annealing work on PLA+ and tough PLA?
Usually, but results vary by blend because the additives change how the plastic crystallizes. Test with a small part first. Colorants and fillers can also affect how much the part shrinks.
How to Anneal PETG
PETG doesn't crystallize, so don't expect the big heat-resistance boost that PLA gets. Annealing PETG is mainly useful to relieve internal stress in functional parts.
- Use a low temperature, around 70–80°C, near PETG's glass transition. Going much hotter makes parts sag.
- Hold for 30–60 minutes, then let the part cool slowly in the oven.
- Support the part well, especially overhangs and thin sections.
If you need more heat resistance than PETG gives you, it's usually better to switch materials than to anneal. ASA and ABS handle much more heat straight off the printer.
Annealing PETG-CF and PLA-CF
Carbon fiber filaments anneal much like their base material: CF PLA like PLA, and CF PETG like PETG. The fibers help limit shrinkage and warping, so carbon fiber parts often hold their shape better during annealing.
Annealing Oven Tips
- A dedicated toaster oven or lab oven works well and keeps plastic out of your kitchen oven.
- A convection or fan setting heats the part more evenly.
- Some filament dryers reach annealing temperatures, but check that yours holds temperature accurately and that the part fits without touching the heater.
- Never leave a part unattended on your first runs until you know how your oven behaves.
Annealing FAQ
What temperature should I anneal PLA at?
Typically 70–90°C for 30–60 minutes, then a slow cool in the oven. Start around 70–80°C and test a small part first.
Does annealing make PLA stronger?
It makes PLA stiffer and much more heat resistant. Toughness doesn't always improve, and annealed PLA can be a bit more brittle. If you need impact strength, try tough, impact-modified PLA or PCTG.
Can I anneal PLA in a regular oven?
Yes, if it can hold a low temperature accurately. Check it with an oven thermometer before you put a part in.
Why did my part warp when I annealed it?
The temperature was too high, the part wasn't supported, or it has thin walls that relaxed unevenly. Lower the temperature, pack the part in salt or sand, and print with more walls and infill.
Should I anneal PETG?
Only to relieve stress in functional parts. It won't raise PETG's heat resistance much. Choose ASA or ABS for high-heat parts.
Not sure which material fits your project? Read PLA vs PETG, or shop 1.75mm filament, made in Indiana, USA.