Has anyone tried annealing 3D prints for increased strength?

Has anyone tried annealing 3D prints for increased strength?

A friend told me about a post process that he has been doing with his prints where he anneals them in hot water.

For example, for PETG he puts his prints in a 160F bath for 7 minutes and claims great results.

I am excited to try when I get home and wondering if anyone else has tried and has further advice.


Annealing is only going to work with specific types of polymers. PLA is one of those polymers. PETG is not (unless there is something special about it). Annealing changes the shape of your print. Usually they shrink. But it’s possible, for example, for it to shrink in length and width but grow in height (example, -8%, -3%, +5%).

Annealing is best used on parts which do not require dimensional accuracy. If you do require dimensional accuracy some vendors sell filament specifically designed for annealing and as such provide geometric percentage variations so that you can adjust your print size to account for the change in geometry from the annealing process.

Any polymer which can be annealed requires that the polymer be of a crystalline structure.

@Greg_Copeland Thanks for the information. Can you post an example of a filament designed for annealing. Thanks

@Jeff_Erenstone I only know of specific PLAs intended for annealing because of some YouTube videos. I do not recall the brands of the filaments used.

Here is a video which tests various filaments. As you can see ABS and PETG did not benefit from annealing.

Here is one example of an “HT” filament designed for annealing: https://www.matterhackers.com/store/3d-printer-filament/graphite-grey-pro-series-ht-pla-filament-175mm

Of course, there are different schools of thought on this too. In that if you want higher temp PLA you should probably be looking at different types of material. But PLA remains easier to print. Thusly the attraction.

The key word is semi-crystalline. Some PLA and certain nylons can form crystal regions which are highly ordered compared to the amorphous region. The drawback is that this causes more shrink. The annealing temp depends on the material. For example, a high temp (HT) PLA is often annealed to achieve better thermal properties after printing.

Nylon will also anneal. It gets more rubbery/tough. Not necessarily something you want.

I am surprised to hear that it has no effect on PETG. My friend did say he does this process with Nylon but also said that it works with PETG (which is my favorite material). Could the process at least reduce stress and strain in the Z layer bonding and have a positive effect on preventing crack propagation in this plane?

BTW: I do a lot of large nozzle diameter vase mode prints.

PETG is a class of compounds, not a specific material. Different PETG filaments may perform differently.

@Ryan_Carlyle That is good to know. Is there a brand that you can reccomend to try annealing with?

@Jeff_Erenstone nope, I’ve only annealed PC personally.

@Ryan_Carlyle Any Luck with PC? Any recommendations with that material?

@Jeff_Erenstone PC is a major pain in the rump to print, but basically you heat it up right below the glass point (130-140C maybe) and it’ll visibly get more transparent and change shape/dimensions a little. I did it in a toaster oven with a thermocouple monitoring air temp. The “low warp” PC blends available these days have lower glass point so it takes some experimenting.

PC gets REALLY strong and tough when you anneal it.

Note that the shrinkage during annealing is caused by strain locked into the print when it cools. For example, if you print fast and small strands, the molecules are all stretched out when they cool solid, and they will try to contract along the length of the strand when annealed.

Also worth noting that different materials do different things when annealed. PLA transitions to a more stable crystalline state. (Harder and more temp resistant, plus volume shrinkage.) PC and nylon become more amorphous. (Tougher and more transparent, with length contraction.) There’s a lot of variability by blends though.

It may be possible to put the print in a metal mold of the right shape and anneal it there, possibly under pressure, to get both dimensional stability and the strength benefits of annealing.

(although at that point you’ve almost reinvented plastic injection molding.)

Stratasys has a patent (surprise surprise) on printing in two materials with different glass points, using the high-temp material to print a mold/support around the low-temp material, and then annealing the low-temp material to strengthen it.

@Jeff_Erenstone I don’t believe it fair to proclaim, “has no effect.” More accurately, it’s simply unlikely to anneal it. As others have pointed out annealing is a specific process which crystallizes regions within the material.

As @Ryan_Carlyle points out (which I had forgotten), there are different types of PETG. Which is why there is a large range of temps used for different PETG filaments. Some print at PLA temps others print in the 250-260 range.

I will offer that when I originally looked into annealing with PETG the general consensus is that annealing PET is possible but the makeup of PETG makes it much less likely. As I lack a chemistry background I do not recall the reasons given.

Cool and thanks for the feedback…I am learning a lot with this thread… keep it come and you all rock!!!

@Greg_Copeland @Ryan_Carlyle or Anyone else.

As mentioned before…it would be really helpful if you could make a specific recommendation on a brand PET or PETG that is worth trying to printing and annealing.

I would like to play but would like to start out in the best direction.


As I’ve not annealed anything and do the bulk of my prints in PETG, I don’t have any specific recommendations.