Annealing PETG: what actually works
Five oven schedules, two filament brands, dimensional measurements before and after. Most internet advice on this is wrong; here's what isn't.
Why bother
PETG comes off the printer well below its full crystalline potential. Annealing pushes molecular reorganization toward equilibrium, gaining heat-deflection temperature, stiffness, and (sometimes) creep resistance. The cost: dimensional change you have to design around.
The schedules tested
I printed 30 identical bend coupons in PolyLite PETG Translucent Blue, divided into five groups, and ran each group through one of these schedules in a convection oven:
| Group | Temperature | Time | Cooling |
|---|---|---|---|
| A | 70°C | 4 h | natural (oven-off) |
| B | 80°C | 2 h | natural |
| C | 90°C | 1 h | natural |
| D | 90°C | 4 h | natural |
| E | 95°C | 1 h | natural |
A reference group sat at room temperature for the same wall-clock time.
What worked
Group D (90°C, 4 hours, natural cool) showed the best balance: ~+18% increase in heat-deflection temperature, no visible deformation on parts ≤80 mm, and dimensional change averaging −0.4% in XY and +0.6% in Z. Group E warped on every coupon — even four-walled rectilinear shapes lost their corners.
What the internet gets wrong
Repeated advice across forums says “anneal in a bed of salt to prevent warping.” It works, but it adds a step that’s mostly unnecessary if you stay under 90°C and use a coupon-friendly geometry. The salt trick exists because people anneal at 110°C; if you anneal at 90°C, the oven by itself is fine.
What’s coming next
I’m running the same protocol on Prusament PC Blend at 105°C and 120°C. Expect that piece in two weeks.
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