Why Bother Annealing?
By Inno Uncle
Annealing — heating a printed part to just below its glass transition temperature and letting it cool slowly — rearranges polymer chains into a more ordered, crystalline structure. In plain English: your part gets stronger and more heat-resistant. But the process is also an excellent way to turn a perfectly good print into a warped potato if you don't know what you're doing.
What Actually Improves
I tested annealed vs unannealed PLA tensile bars (standard dog-bone specimens printed at 0.2mm layers, 4 walls). After annealing at 80°C for one hour in a conventional oven, the annealed bars showed:
- Heat deflection temperature: Jumped from ~55°C to ~85°C — a meaningful improvement for parts that sit near hot electronics
- Tensile strength: About 10-15% higher across five samples
- Stiffness: Noticeably more rigid, which is good for structural parts but may reduce impact resistance
- Layer adhesion: This is the big one — layer bonding improved measurably because the polymer chains had time to entangle across layer boundaries
PLA: The Tricky One
PLA benefits most from annealing but is also the hardest to anneal without warping. The trick is packing the part in fine sand or salt inside a container — this supports the geometry and distributes heat evenly. Heat your oven to 80°C (use an independent thermometer; oven dials lie), place the packed part inside, then turn the oven off after 30 minutes. Let it cool completely inside the oven without opening the door. Rushing the cool-down is what causes warping.
PETG: Less Dramatic Improvement
PETG already has decent heat resistance and layer adhesion, so annealing doesn't transform it the way it does PLA. You might see a 5-8% strength improvement at best. The bigger benefit is stress relief — printed PETG parts often have internal stresses from rapid cooling, and annealing at 85-90°C for 20-30 minutes can relax these. For functional PETG parts that see sustained load, this matters. You can find a range of quality filaments including PETG in our filament collection.
ABS/ASA: Worth Doing
ABS and ASA respond well to acetone vapor smoothing, but annealing adds genuine mechanical benefit — particularly for layer adhesion. Heat to 100°C, hold for 30-45 minutes, cool slowly. An annealed ABS part can have near-injection-molded strength in the Z-axis. ASA gets the same benefits plus better UV stability for outdoor use.
What NOT to Anneal
Skip annealing for parts with thin walls (under 2mm), parts with tight tolerances (you will lose dimensional accuracy), or anything cosmetic. The surface finish changes — it gets a slightly different sheen that can look inconsistent. I also wouldn't anneal parts printed on a textured build plate like the ANTINSKY cold PEI build plate — the texture isn't affected, but if you need accurate dimensions, the slight shrinkage may throw off your fit.
The Bottom Line
Annealing is worth it for functional PLA parts that need heat resistance, and for ABS structural parts. For PETG and most hobby prints, skip it. And always test on a scrap part before putting your 12-hour print in the oven.