This month we tackle a common request: Metals in PETG. We've pushed back asking, " Why PETG when heat-treated HTPLA is so much more temperature resistant?" Well, PETG fans, this one's for you!
Introducing Iron, Stainless Steel, and Copper PETG Composites.
All are 60 wt% metal, but the first thing we noticed is you can bend metal composite PETG without breaking. PETG metals are much less fragile. Breaking without much bending is one of the biggest criticisms for metal HTPLA and PLA. You do have to take more care when handing metal PLAs.
I guess this attribute shouldn't be so unexpected, but it is refreshing. Otherwise, you've got the typical attributes you'd expect from PETG and metal composites.
- We used glue stick for the best grip when using Generic PETG settings.
- Co-polyesters like PETG can stick to the nozzle. Drying, reducing flow, and/or choosing a nozzle with slick coating like Obxidian from E3D can reduce sticking.
- PETG metals are about 2x as dense as PETG alone, so you get half the length.
- PETG metals can be finished like metal PLAs which finish like metal.
Here's an old "How-to" we've updated with some sample finishes.
When oxidizing, start with salt and water or hydrogen peroxide. That's all you need for iron, but vinegar and/or ammonia can add oxidation and color, especially for copper, brass, and bronze. Try separately or combine. The best results come to those who patiently reapply a small amount often like with a paint brush. This allows the oxidation to build up and stay with the print rather than washed away. Heidi prepared a grid with a variety of chemicals.
Brass, bronze, copper, and iron from top to bottom. Sanded with no chemicals, hydrogen peroxide, vinegar, ammonia, and sulfuric acid from left to right. Corey puts prints in a container to keep them immersed in vapor. There's lots of ways to oxidize. Here's a look at one of Corey's metal finishing videos where we uses a spray bottle.
When polishing, take your time. Start with a coarse grit (200-300) to sand away layer lines. Gradually work to finer grits. I typically finish by hand up to 6000 grit with 3M polishing paper, but there are many products and methods to choose from. The trick is not building up too much heat or moving to the next grit before the previous grit lines are removed. Heidi prepared the below grid with finer grits as you go down towards the bottom. Look closely and you can see a reflection on the bottom row. Best seen in person to appreciate. Maybe you'll come see it in person at 3D Printopia?
Boss level goals? Eric created a jig and polishes flat surfaces using a drill press. The result is almost unbelievable, but it's real! Really good!!! Extra points to Eric for putting a magnet in the fixture to hold the is stainless steel print. Yes, it's stainless steel and magnetic. 400-series. Not familiar? Look it up! :-)
To wrap up this exploration, we had to see how strength compare to our metal PLAs. Both Iron and Copper 1.75 mm PETG filaments had an ultimate tensile strength of 45 MPa. Steel's was 40 MPa. Comparing to our 2025 blog with PLA + HTPLA metal data, these PETG metals are now our strongest metal composites! They are also more ductile (see the tail to the right of the peak in chart below). Great to know, right? And they have heat resistance in between PLA and heat-treated HTPLA but without having to heat treat. Very cool!
Magnetism will be comparable to 60 wt% Steel and Iron PLAs, more specifically High Density Iron HTPLA and our original Stainless Steel PLA. High Density Stainless Steel HTPLA has our highest metal loading at 70%. That's going to make it the most magnetic, but it also has the lowest ultimate strength. See all our metals in the Metals Collection.
Well, I think that covers everything for this month.
Take care and enjoy the pasta,
Alex and the Protopasta Team
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I can't wait to see what you print with these. Whatever you make, I hope you are inspired by these fun filaments! Tag Protopasta to show us what you make!!!
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Protopasta is 100% made in the USA by Protoplant Inc. Founded in 2013 by engineers, Dustin and Aaron Cram, we control every step of the process with in-house made machinery and materials. We’re a small team with a passion for making things, just like you! We’re here because of you. We’re here for you. Thank you for choosing Protopasta!