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Guide to 3D Printing with U-HIPS Filament

Here at CLP we strive to bring you high quality 3D printing filament made from 100% post-consumer plastic waste that’s easy to use and can drop right into your current 3D printing workflow.


1kg spool of CLP U-HIPS filament in Nebula Black under a wavy vase printed with U-HIPS filament

But we understand that you might be a little hesitant to try a new material, especially one made from trash, so we wanted to provide you with some background on HIPS material and how it prints, but more importantly give you some suggestions on how to make it work best for you.


So let’s get started!


What is HIPS

HIPS (also known as PS) stands for High Impact Polystyrene. HIPS material is an amorphous thermoplastic, which means it softens and is more pliable with the introduction of heat. This is why this material works well with 3D printing, since that’s exactly what the hot-end is used for!


One thing to note about HIPS material, however, is that it does exist in both rigid and expanded form, both demarcated by the recycling number 6. Rigid HIPS, which is what makes up many to-go plastic food containers, coffee lids, disposable cups, etc. is the type of material we process at CLP and the type of material that’s printable. Expanded HIPS (EPS) is what we know as styrofoam, which is not a 3D printable material.




Properties

In terms of properties, HIPS behaves similarly to ABS (acrylonitrile butadiene styrene) which is a material commonly used in many injection molded and 3D printed parts. It has high impact strength (hence the name), good dimensional stability, high stiffness, and best of all, it’s recyclable!


Its high impact strength makes it a durable material and can withstand higher impact than other materials like PLA. For context impact resistance is measured using an American Society for Testing and Materials (ASTM) standard test known as the izod impact strength test, which measures the amount of energy required to break a standardized notched sample of a given material. A pivoting arm machine is brought down on the sample and the energy that’s absorbed is measured. As an example, HIPS izod impact is measured to be 2.8 ft-lbs/in (Source) whereas PLA izod impact is measured to be 0.3 ft-lbs/in (Source), which means it requires around 9 times more energy to break HIPS than it does to break PLA.


Another benefit to using HIPS material is that it’s non-hygroscopic, which means it doesn’t absorb moisture from the air as readily as other materials. This helps with preserving the shelf-life of your filament. Of course, for best performance, you’ll still want to ensure the reduction of moisture contact with the filament while it’s being stored. For our tips and tricks on how to do that, check out our article on filament storage.


And of course, the recyclability of HIPS material goes a very long way. HIPS can be mechanically recycled yet still maintain 99% of its original mechanical characteristics. Which means that the quality of the material essentially doesn’t degrade, making it an ideal plastic for recycling and 3D printing!


Some Drawbacks

Before we convince you that HIPS is an awesome all-magical material, it’s important to also consider the drawbacks of using HIPS for 3D printing. Because the required printing temperature of HIPS is higher than other materials, this makes it susceptible to a high temperature differential as it’s being printed. This can cause inconsistent cooling, which can lead to delamination.

We recommend either printing with an enclosure to reduce the severity of the temperature differential, and/or slowing the print speed to assist in reducing delamination.


While on the topic of printing temperatures, HIPS should be printed at a temperature around 220°C-245°C. Since this is higher than other common printing materials like PLA (190°C-220°C), this also requires more energy and can be harder on the printer.


Another potential drawback to HIPS material is that it has a high stiffness. Even though that can be a positive feature for items that require the model to be stiff, this also makes it susceptible to breakages.

To reduce the possibility of brittle breakages occurring, we recommend adding at least 3 or more outer/vertical perimeters. Another adjustment can be in the model itself, by smoothing the curves of the main geometry of the part and avoiding hard edges if possible.


Printer Troubleshooting Tips

Now we want to discuss some common troubleshooting issues that you may encounter when printing with HIPS. Here are our best tips for how to address these issues.


Temperature

Keep in mind that HIPS is a fast-cooling thermoplastic. Without adjustments, the layers may not fuse evenly or properly, which can be seen in the sample prints below. For proper bed and layer adhesion, a higher nozzle and print bed temperature are recommended. Using enclosures for your prints can also help.


Sample 3D prints in U-HIPS material
The uneven temperature differential affects layer adhesion

Speed

Because of the fast cooling, slower printing speeds are recommended for optimal results (less than 60 mm/s). We also recommend avoiding fast travel speeds due to the differential cooling.


Bedplate Adhesion

When it comes to bedplate adhesion, we know everyone has their favorite tried and true methods. For printing with HIPS, we recommend printing with a brim and experimenting with other third party materials like Magigoo. And because of the temperature differentials that HIPS experiences while it cools during printing, remember that a heated bed printer is required.


3D print with edges lifted from the bedplate
What may occur if you don't pay attention to bedplate adhesion

Model Design

As we mentioned earlier, HIPS stiffness, while great for durability, can also lead to brittleness. Printing sharp details may result in less optimal outcomes, so we would recommend avoiding hard edges if possible in your model design. This applies not just to U-HIPS material but other 3D printing materials as well.

Smoother edges make for smoother-looking prints and help prevent corner breakages


Post-Processing

For additional post-processing needs, the following are the methods that work really well with HIPS material.


Acetone Finishing

Since HIPS is dissolvable in acetone, acetone finishing is a great way to smooth out your print. As a word of caution, please work with acetone very carefully. It is a highly flammable solution and should be worked with in a well-ventilated area.


An example of acetone finishing. Photo by Wikimedia Commons.

Sanding and Priming

Similar to other materials, HIPS is very receptive to sanding followed by priming to create a smooth finish. Though it’s also important to keep in mind that over-sanding can cause deformation from the friction and thermal transfer.


Use Cases

U-HIPS filament can be used for any number of practical prints and other applications. Just check out our Practical Print series if you need some ideas!


Here are some other notable use cases:


Scaled Godzilla Model

To really put U-HIPS to the test in terms of its ability to print detailed objects, we printed a scaled Godzilla model. This print in total took 29 hours because of the amount of detail in the object. Even though this print could have been sped up, we maintained the print speed at 60 mm/s to allow for enough cooling time.


To maintain bedplate adhesion, we used Magigoo to keep the feet and tail in place while printing since this print wasn't printed with any support material. We also used a brim to ensure there was as much first layer surface area as possible. We also made sure to not have the fan on at any point to minimize any delamination.





Beard Comb

This model, printed by co-founder Will Amos, showcases a lot of aspects about HIPS material. It’s durable and rigid so the comb tines don’t flex when they’re being used to comb through hair.


Isometric view of 3D printed beard comb made out of pink U-HIPS filament
Beard comb printed with U-HIPS material


Hand Planes

A great example of some stellar priming can be seen in one of our Customer Spotlights with Bill Raymont of Perpetual Use Plastics. His handplanes were printed with our U-HIPS filament, then he post-processed them so they would be smooth and water-resistant so he could use them in the ocean.




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