At Filabot, we’re big believers in closing the loop. Post-consumer plastics don’t need to stop at the recycling bin, they can find a second life as fresh, functional 3D printer filament. Not every plastic is suitable for this process, but several common ones can be recycled into filament without additives.
Before we dive into the workflow, let’s take a step back and look at all seven resin codes that define consumer plastics. Understanding what each code means is the first step toward knowing which plastics can become usable filament.
Understanding the 7 Plastic Recycling Codes
If you’ve ever looked closely at a plastic container, you’ve probably noticed the little recycling triangle with a number inside. Those numbers, 1 through 7, tell us what type of plastic we’re dealing with. And for anyone interested in recycling plastics into 3D printing filament, they’re more than just symbols. They’re a roadmap to what works, what doesn’t, and what needs extra care.
Here’s a quick overview:
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#1 PET (Polyethylene Terephthalate) – Most commonly found in water and soda bottles. It’s strong and clear but crystallizes too quickly to make good filament on its own. Modified versions like PETG are widely used in 3D printing.
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#2 HDPE (High-Density Polyethylene) – Think milk jugs, detergent bottles, and piping. It’s lightweight and chemical-resistant. It can be turned into filament, though it tends to warp during printing.
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#3 PVC (Polyvinyl Chloride) – Pipes, flooring, and some packaging. It releases toxic gases when heated and is not safe for filament extrusion or printing.
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#4 LDPE (Low-Density Polyethylene) – Found in plastic bags and squeezable bottles. Flexible and soft, it doesn’t hold shape well as filament.
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#5 PP (Polypropylene) – Common in food containers, caps, and straws. It’s durable and light. It can be extruded into filament, though like HDPE, it’s tricky to print due to shrinkage.
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#6 PS (Polystyrene) – Disposable cutlery, CD cases, and foam packaging. Too brittle for reliable filament, unless blended with other resins.
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#7 Other – A catch-all category that includes ABS, polycarbonate (PC), nylon, and blends. Some of these (ABS, PC, Nylon) are excellent for filament and need no additives. Others are layered composites that don’t reprocess well.
So, while not every plastic can become usable filament, several of them, especially HDPE, PP, and ABS, can be recycled directly into spools without additives. The challenge is less about whether they can be extruded, and more about how well they print.
Why HDPE, PP, and ABS?
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HDPE (High-Density Polyethylene) – Found in milk jugs, detergent bottles, and piping. It’s tough, lightweight, and resistant to chemicals.
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PP (Polypropylene) – Common in food containers, caps, and automotive parts. Known for fatigue resistance and versatility.
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ABS (Acrylonitrile Butadiene Styrene) – Used in housings, toys, and countless consumer products. Strong, durable, and already a staple in the 3D printing world.
These three plastics share something important: they can be extruded into filament without blending in additional materials. That doesn’t mean they’re all equally easy to print, each comes with quirks like warping or moisture sensitivity, but the base resins are capable of becoming filament on their own.
The Workflow: From Waste to Filament
Recycling into filament isn’t just about melting plastic down. To get reliable, high-quality filament, there’s a process, one that emphasizes cleanliness, consistency, and control. Here’s a step-by-step breakdown:
1. Collection & Sorting
The first step is making sure you’re working with the right plastic. Sort post-consumer waste by resin code: HDPE (#2), PP (#5), or ABS (#7). Mixing different polymers leads to poor bonding and inconsistent extrusion. For example, HDPE and PP are immiscible, they simply won’t blend well. A simple float test helps: HDPE and PP float in water, while ABS sinks.
2. Cleaning & Drying
Wash thoroughly to remove labels, food residue, or adhesives. Contamination is the fastest way to ruin a batch of filament. Drying is critical:
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HDPE & PP: ~80 °C for 2–4 hours
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ABS: ~80–90 °C for 4–6 hours (more hygroscopic than the others)
Moisture left in the plastic can create inconsistent extrusion, bubbles, weak spots, and poor surface finish.
3. Shredding & Pelletizing
Once clean and dry, plastics need to be reduced in size. A granulator or shredder turns bottles, containers, or parts into flakes. For the best extrusion consistency, those flakes can be pelletized — uniform pellets feed more smoothly through an extruder screw and help maintain stable filament diameter.
4. Extrusion Into Filament
Now comes the fun part. Using a filament extruder like the Filabot EX6 or industrial-scale equipment from Massive Dimension, you can reprocess the prepared feedstock into filament. Each plastic runs at a different temperature window:
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HDPE: 200–230 °C
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PP: 200–220 °C
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ABS: 230–250 °C
A melt filter screen (60–100 mesh) helps trap impurities, and precise screw design ensures the melt stays uniform. As the filament leaves the extruder, it’s cooled in air or a water bath, then pulled at a controlled rate to maintain a consistent diameter.
5. Spooling & Quality Control
Filament is only as good as its consistency. Real-time diameter monitoring (laser micrometers are ideal) keeps filament within ±0.05 mm tolerances. After extrusion, spool the filament under controlled tension. Run QC checks for roundness, brittleness, and test prints to verify performance.
6. Storage & Labeling
Store your spools in airtight containers with desiccant packs, especially ABS, which absorbs moisture from the air. Always label spools with resin type and batch info so you know exactly what’s on hand.
What to Expect When Printing
Each plastic brings its own behavior in the printer:
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HDPE & PP – They extrude beautifully but tend to warp and shrink during printing. Heated chambers and special build surfaces are often required for successful prints.
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ABS – The most user-friendly of the three for printing, though it does produce fumes and requires ventilation.
Even with their quirks, all three can be recycled directly into filament. That’s a win for reducing waste and expanding what’s possible in recycled 3D printing.
Closing the Loop
Turning post-consumer plastics into filament is more than just recycling, it’s about building a circular workflow for materials. With the right preparation and the right tools, you can transform common waste streams into high-value feedstock for 3D printing.
At Filabot, we design extrusion systems to make this process accessible, from benchtop experiments to scaled production. Whether you’re recycling HDPE from milk jugs, PP from food containers, or ABS from old electronics housings, the process is within reach.
Let’s close the loop, one spool at a time.
