Endless Exploration EX3 (July 2024) TPE & TPU materials

In our first two Endless Explorations, we explored high speed and low gloss PLAs. For EX3, we chose some materials that process near PLA temperatures with near PLA ease, but offer different properties from different chemistries. While printing a bit differently than PLA, a good result is possible with TPE and TPUs. 

What are TPEs and TPUs?

TPE means Thermoplastic Elastomer. TPU means Thermoplastic Polyurethane. Both are known for being synthetic, rubber-like, resilient materials, but are broad categories with a wide range of attributes like translucent or opaque, hard or soft, and flexible or rigid. Cost as well as heat and chemical resistance also vary.

For this exploration, Flexible TPE (black) is Polyester, Flexible TPU (clear) is Polycaprolactone (similar to Polyester), and Rigid TPU (white) is Polyether-based. We made each a different color to more easily identify each one. It’s worth noting that the varied chemistries lead to varied performance. All 3 materials are unfilled and not abrasive. They are also low odor and safe to handle.

Protognomes printed at min 1, max 3 mm^3/s, 100% fan, & 240 C on Bambu P1S

Flexible TPE (black) has minimal moisture sensitivity. We found drying was not required. Flexible TPE reached the highest rate, 16 mm^3/s, of these 3 materials at 240 C nozzle on the Bambu Lab P1S with 0.4 mm steel nozzle printing  2-12 mm^3/s and 14-24 mm^3/s D-shaped rings like in EX2.

Flexible TPE's speed is cooling limited and must be reduced for small cross-sections. Luckily, the materials lack of moisture absorption allows for low printing rates. Using 100% fan and no bed heat optimizes detail, but detail is somewhat sacrificed with short layer times (as seen in the gnome above) compared to TPU.

TPE had a higher tendency towards jamming, specifically when starting a new print right after one was finished. When unloaded after a print or after jamming, inspect the filament end for defects. If a defect is present (like below), remove it before reloading to start a new print.

We did not find disassembling the hotend necessary to recover from jamming, but we did sometimes experience repeat jams with previously successful conditions. In this case, we loaded another material like PLA to clear the hotend before swapping back to TPE.

We persevered with a stock 0.4 mm nozzle, but it's possible (even likely based on past experience) that a larger nozzle or different nozzle type may be more forgiving. We did make some good prints with a 0.8 mm nozzle, but we have not quantitatively investigated alternate nozzles.

Printing these materials can be challenging so deep breaths, breaks, and snacks are also recommended!

Flexible TPU (clear) is more print rate limited, but less cooling limited compared to TPE. TPU produces better detail with less surface defects at low rates. Flexible TPU reached 8 mm^3/s at 240 C nozzle on Bambu P1S with 0.4 mm steel nozzle. Flexible TPU is somewhat moisture sensitive, but a good result was possible without drying. No bed heating was required for warp-free printing.

Printing hotter allowed higher rates. Flexible TPU reached 12 mm^3/s at 260 C and 24 mm^/s at 280 C. While the higher nozzle temp increased the maximum rate, you can see the hazy, bubble-filled cross-section at 2 mm^s where the Flexible TPU is getting overheated at this low rate (below). In contrast, 4 mm^3/s and above, the cross-section looks clear and free of inclusions.

Rigid TPU (white) is more nylon-like than rubber-like, and it was the most challenging to get a good printing result until we dried the filament. Once dried, Rigid TPU performed well, and it did not require re-drying to retain reliability. The operating range was similar to Flexible TPU with an 8 mm^3/s limit at 240 C nozzle on Bambu P1S with 0.4 mm steel nozzle. This is the limit with 100% fans.

Beware - setting changes (like temp, rate, and fan %), setup (like build prep and conditions), and hardware changes (like nozzle material and opening) can impact results.

Printing with Rigid TPU before drying resulted in under-extrusion and jamming. After jamming, material must be unloaded to remove defects before reloading to start a new print. Failing to remove defects will lead to under-extrusion when starting a next print. Jamming could be avoided without drying by increasing nozzle temperature, but this introduced bubbles and stringing.

We dried Rigid TPU overnight in our Eibos Series X: Easy Dry on the TPU setting. Drying allowed a lower nozzle temperature without bubbles, stringing, or jamming.

TPE and TPU can ruin build surfaces! To avoid this, use an intermediary product like Magigoo. Magigoo will peel away from your printing surface when cool while your flexible filament without Magigoo may not. Because it peels away, you will need to reapply where prints are removed.

A sample of Magigoo was provided to all Endless Exploration Subscribers and is available at Protopasta.com in the Accessories Collection.

The above recommendations are based on our experience with Bambu P1S 3D printers. Your experience may vary. We invite you to explore by repeating our tests and/or make your own. Please also share your results so we can all learn more together!

Continue for more testing results...

We tested temperature performance in our lab oven too. We added parts and set our lab oven to 475 deg F. The oven temp increased at about 10 deg F/minute. At that rate, Flexible TPE held shape until about 300 deg F (150 deg C). Both TPUs held shape until about 390 deg F (200 deg C). That's hotter than boiling water!

It’s possible parts would lose shape at a lower temperature with a less than 10 deg F/minute rate and/or in another medium than air (like water), but this test demonstrates thermal performance of a non-functional part with no load. Part performance will decrease as temperature increases, and it will be geometry and load dependent.

Because these materials can survive temperatures above boiling, we tested coloring them with RIT DyeMore. In their uncolored form, all 3 materials could be colored with boiling hot dye. We also tried dying at room temperature, but this proved ineffective. Below is our dyeing method:

We started with ½ tsp of dye for 8 oz near boiling water per the RIT label in glass mason jars. We waited 30 minutes. Black and blue were pretty dark, but could be darker. Red and yellow could be much more dark.

We emptied the jars, shook the RIT bottles, and increased the concentration. This time we decided how much dye to add by judging the darkness of the solution. We carefully boiled the water + dye mixture in the microwave. Use caution when boiling water in the microwave! We microwaved the solution 30 seconds at a time and found only about 2 minutes was required. Result as shown.

We also wanted to find out how rubber-like and resilient these materials are. We did so by printing balls the same weight and size as racquet balls (2.25” & 40g). The TPUs bounced less TPE for more damping (vibration absorption).

We also printed thin 0.4mm thick sheets to fold. The TPUs had the best return when folded with no permanent crease, and returning to their original shape without assistance. What great memory retention! Flexible TPE had a permanent crease in 0.4mm sheets and did not return as flat as Flexible TPU. Still, all 0.4mm sheets could NOT be broken when folded 180 degrees back and forth indefinitely.

In the end, all 3 materials proved to be quite resilient and would make good living hinges (unlike PLA and PETG)! Shout out to Joan Horvath at Nonscriptum. We printed geometric shapes designed by her business partner, Rich Cameron. These shapes are from Make: Geometry. Yes, we printed geometric shapes to celebrate!

To print the above, all 3 materials were run with 20 C bed and limited to 8 mm^3/s volume rate. The previously dried Rigid TPU was printed at 240 C while the Flexible TPE and TPU we're printed at 260 C to avoid jamming and stringing, respectively, which was experienced at 240 C. Prints are about 20g and took less than 1 hour to print. All have 0.4 mm thick (2 layers) living hinges that performed well with good durability, but variable return as seen in the above video!

As previously mentioned, the different chemistries lend to different chemical performance. While I can’t find details regarding the chemical performance of TPE, it's generally said to be chemically stable and non-reactive with metals. TPE should perform from well below freezing to near boiling of water.

The TPU materials should perform well in a similar thermal range. I have more extensive chemical resistance data for polyester (like Flexible 98A) and polyether (like Rigid 70D) to share from the chemical manufacturer, Lubrizol. Here are Lubrizol's Flexible 98A and Rigid 70D technical data sheets as well.

Rigid TPU (70D Polyether) is formulated for UV stability as well. It's UV stability, chemical resistance, and no warp printing make it an excellent candidate for replacement difficult-to-print performance polymers like nylon and polycarbonate.

In fact, one user found Rigid TPU's resistance to wear and chemical resistance to exceed that of machined Delrin or UHMW. 3D printed Rigid TPU is also lower cost to produce, printable on low cost, consumer machines like the Creality Ender 3.

In summary, these TPU and TPE materials are highly durable with great potential for applications with requirements that exceed what's possible with PLA or PETG. Thanks to Endless Exploration subscribers for supporting this new development!

What will you print? Show us on social (links below).

Not an Endless Exploration Subscriber? Subscribe for the next delivery (topic: glow-in-the-dark) and/or purchase the TPU/TPE materials individually in August.

Take care and enjoy the pasta,

Alex and the Protopasta Team

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