What is Polyethylene?
Polyethylene is a form of thermoplastic that is widely used in a variety of different forms. It can be categorised into a few forms such as Low-Density Polyethylene (LDPE), High-Density Polyethylene (HDPE) and as a polymer Polyethylene terephthalate (PET).
It is extremely recyclable and is widely used in various forms in everyday objects such as plastic bottles and milk cartons.
You can 3D print Polyethylene, with HDPE and PET being the two most common forms of Polyethylene filament. The filament itself is normally used with FDM 3D printers and has some unique pros and cons for why you should or shouldn’t use it.
An introduction to HDPE
HDPE is the form of Polyethylene that is commonly used in milk cartons and drink bottles. Unlike PET, HDPE isn’t completely clear and is slightly opaque. It does feature a really good amount of strength compared to its weight. This allows HDPE objects to float in water.
You can 3D print HDPE, but it does come with some challenges, which is why it isn’t widely used as a 3D printer filament.
3D Printing with HDPE
While 3D printing with HDPE is very similar to ABS, it does present a number of challenges. HDPE requires you to have a relatively high nozzle temperature between 220°C and 260°C. While many home 3D printers will be able to achieve this heat, some won’t so double check if your printer nozzle can achieve this heat.
The same heat issue applies to your print bed. To achieve the most success you will also require a hot print bed to give your 3D printed object the best chance of adhering.
The main problem that high-density Polyethylene suffers from is a lack of adhesion. This is why you require a hot print bed. However, you can also run into problems caused by the layers not correctly adhering to each other during the 3D printing process.
You need to ensure your print bed is as stable as possible, and it is recommended that you print at a slower speed for the best chances of success.
You will also need to be aware of your 3D print shrinking while cooling. This occurs specifically with HDPE, but can cause warping or cracking if it happens too fast. It would be better to ensure the ambient temperature isn’t too cold during the printing process. And allow your HDPE 3D print to adjust to cooler temperatures slowly.
Once fully printed and cooled though, HDPE will have similar characteristics to ABS. Although it will be slightly stronger and more lightweight.
HDPE pros and cons
Pros
- Great strength – HDPE is stronger than other filaments such as ABS. Due to its fantastic strength to density ratio, it can produce strong 3D printed objects without too much excess weight and filament usage.
- Extremely lightweight – As mentioned above, HDPE has a fantastic strength to density ratio. The lightweight nature of HDPE allows it to be light enough to float in water.
- Not water-soluble – HDPE can be completely watertight, and doesn’t dissolve in water. This makes it great for applications such as holding liquids or use with water-based objects.
- Dissolves in Limonene – Despite being non-water-soluble, HDPE does dissolve when exposed to Limonene.
- Recyclable – Polyethylene is highly recyclable. You can shred larger plastic items to recycle HDPE or other types of Polyethylene, and reuse them again.
Cons
- Harder to 3D print with – HDPE has a high melting temperature meaning it has the requirement of a hotter extruder nozzle and print bed.
- Hard to come by – Due to its tricky nature when being used as a 3D printer filament, HDPE can be hard to find and purchase.
- Can warp when printing – HDPE suffers from low adhesion, making it fairly tricky to achieve successful 3D prints. You can often find layers won’t fully adhere to each other which in turn can make your 3D print warp.
- Shrinks when cooling – During the cooling process directly after 3D printing, HDPE will shrink slightly. This can affect and compromise the strength of your final 3D printed object.
Is HDPE recyclable?
High-density Polyethylene is widely recyclable, making it a fantastic filament to 3D print with. While you can’t recycle HDPE yourself, you can send it off for recycling where it will be cleaned, shredded into pellets and reformed.
Where to buy HDPE filament
As mentioned, HDPE is extremely hard to come by due to not many people 3D printing with it. However, you can purchase PETG (Polyethylene Terephthalate combined with Glycol) which has similar characteristics to HDPE.
What’s the difference between HDPE and PET?
PET (Polyethylene Terephthalate) is a much more commonly used form of Polyethylene. Although PET isn’t overly used in its raw form, PETG is widely used. PETG is Polyethylene Terephthalate combined with Glycol. This modification removes some of the negative features of raw PET and also makes the filament clear once printed.
3D Printing with PETG
Much like HDPE, PETG is widely used in plastics and water bottles and is actually one of the most commonly used types of plastic. It is quite strong and durable when compared to PLA, and it has good impact resistance.
Unlike HDPE, PETG doesn’t shrink as it cools, making it much easier to 3D print. It behaves very similar to ABS, with good strength and flexibility, and it is slightly easier to 3D print with compared to ABS.
PETG pros and cons
Pros
- Good strength – Similar strength to ABS filament.
- Flexible – While not entirely flexible, PETG does have improved flexibility over PLA, making it more durable over time, and more likely to maintain its form under heavy load.
- Transparent – Due to the added Glycol, PETG is almost entirely transparent, making it perfect for water bottles.
- Waterproof – Much like HDPE, PETG is also waterproof. This allows you to 3D print entirely watertight objects.
Cons
- Bad adhesion – Unfortunately, much like HDPE, PETG also suffers from a lack of adhesion. This can make 3D printing with it slightly harder than PLA.
Where to buy PETG filament
PETG is one of the most widely used 3D printing filaments. It sits alongside PLA and ABS as one of the big three filament types. This makes it readily accessible and easy to find.
Learn about other 3D printing materials in our complete 3D printing material guide.
