How to Anneal Tough Pro PLA+ for Heat Resistance

Short answer: pack your Tough Pro PLA+ part tightly in plaster or salt flour (a very fine salt powder), bake it at 110-120 °C for about 20 minutes (for 3.2 mm walls), then let it cool at room temperature. As printed, Tough Pro PLA+ softens around 55-60 °C. After annealing it holds its shape up to 75-85 °C. Expect about 1-2% shrinkage.

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Why anneal Tough Pro PLA+?

Tough Pro PLA+ already handles heat better than standard PLA straight off the printer, and it has 8.8x the impact toughness of our Standard PLA+. Annealing takes it further. A part that would start to soften at 55-60 °C as printed can hold its shape at 75-85 °C once annealed, and it gains impact strength too.

That matters for parts in a car interior, near motors or lights, or left in the sun.

Why Tough Pro PLA+ anneals and most PLA doesn't

Fresh off the printer, PLA is mostly amorphous: the molecules are frozen in a tangle because the plastic cooled too fast to organize. Annealing heats the part above its softening point, but well below its melting point, and holds it there long enough for the molecules to line up into crystals. A more crystalline part keeps its shape at much higher temperatures.

Not every PLA can do that. Tough Pro PLA+ is made in Fargo from NatureWorks Ingeo 3D870, a grade designed for 3D printing that crystallizes when heat treated. Most PLA and PLA+ on the market, including our Standard PLA+, is made from general-purpose resin and tends to slump or warp in the oven instead.

What you need

A part printed in Tough Pro PLA+
An oven or toaster oven, plus an oven thermometer (oven dials are often off by 10-20 °C)
Plaster of Paris, or salt flour (a very fine salt powder)
A metal or glass container a little larger than the part (for large parts, an aluminum jig)

How to anneal Tough Pro PLA+, step by step

Print the part. Use our Tough Pro PLA+ profiles, or 230-250 °C on a PLA profile. If dimensions matter, scale the model up 1-2% to make up for shrinkage, then confirm with a test part.
Measure it. Note the key dimensions so you can check shrinkage afterward.
Pack it tightly. Set the part in the container and pack plaster or salt flour around and inside it so every surface is supported. Support is what keeps the part from warping.
Preheat to 110-120 °C. Check the temperature with your oven thermometer, not the dial, and check a few spots in the oven for hot or cold areas.
Bake. About 20 minutes for a part with 3.2 mm walls. Thicker parts, and packed parts, need longer for the heat to reach the core.
Cool at room temperature. Let the part cool before unpacking it, and handle it as little as possible. The inside stays hot longer than the outside.
Unpack and check. Brush off the packing material and measure the part again.

What to expect

Heat resistance: 75-85 °C (HDT at 0.45 MPa, ASTM E2092) after annealing, up from a 55-60 °C softening point as printed.
Shrinkage: about 1-2%. Long, thin or unsupported features can still move, so test any part that has to fit.
Finish: parts often turn more milky, matte or opaque as they crystallize. That's normal.

Full test data is on the Tough Pro PLA+ technical data sheet.

Why we no longer recommend a water bath

Boiling water tops out at 100 °C, below the 110-120 °C that Tough Pro PLA+ needs, and a part in water has nothing holding its shape. The packed-oven method gives you the right temperature and the support to keep the part true.

Do you need to anneal at all?

Often not. Customers use Tough Pro PLA+ unannealed in hot cars, and it's tough straight off the printer. Anneal when a part has to hold its shape above about 60 °C. If a part will live outdoors in the sun or around chemicals, Pro PCTG may be the better material. See our PCTG guide.

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Annealing FAQ

Can you anneal PLA+?

It depends on the resin, because "PLA+" has no fixed definition. Tough Pro PLA+ is made from NatureWorks Ingeo 3D870 and anneals well. Most general-purpose PLA and PLA+, including our Standard PLA+, deforms instead.