Polypropylene 3D Printing Guide: Compare Processes, Materials, and Applications

Polypropylene (PP) is a polyolefin similar to polyethylene. It is a thermoplastic used in the manufacturing and consumer goods industries for the mass production of common items like plastic bottles. Polypropylene is formed by chain-growth polymerization of a single propylene monomer. It is extremely similar to another common commodity plastic, polyethylene. The two materials are sometimes combined during recycling processes to produce recycled polyolefin fibers. Though polypropylene was first developed in 1951 by American employees of Philips Petroleum, research and development are ongoing, and there is much promising research on bio-based polypropylene materials as well as novel recycling techniques. 

Polypropylene’s ductility, lightweightness, and chemical and water resistance make it ideal for consumer goods where walls are thin, but strength is necessary, such as in plastic food containers. Its most common use is for bottles of liquids like shampoo, motor oil, cleaning solutions, and others, as well as for laboratory tubes and bottles, food and pharmaceutical containers, and medical devices. A common use case for polypropylene materials is in the fabrication of plastic window shades. 

Polypropylene’s ductile qualities make it ideal for the production of parts that have living hinges, such as the lids of candy containers or shampoo bottles. PP resists fatigue and can be used repeatedly even in these applications.

Polypropylene materials are lightweight, watertight, chemically resistant, and ductile. The density of polypropylene is low, typically between 0.895 and 0.93 g/cm³, making it one of the lowest-density plastics available and thus well-suited for lightweight applications.

Polypropylene has good thermal resistance as well as hydrophobic and oleophobic qualities, leading to its common use in the food packaging industry. When combined with other compounds, polypropylene can become quite tough and be used for engineering applications where repeated pressure or impact occurs. The heat deflection temperature (HDT) of many forms of polypropylene materials is about 100 °C at 0.45 MPa, which, though not extremely high, makes it suitable for a wide range of applications. 

Polypropylene powder, while not the most common material used for SLS 3D printing (which is nylon), is still a very popular material offered by industrial SLS 3D printer manufacturers. Polypropylene’s ubiquity in the commodity plastics market means that for any manufacturer looking to offer end-use production solutions, polypropylene is a must-have material. Some entry-level SLS desktop or benchtop machines do not offer polypropylene powder, while most major industrial solutions do. 

Formlabs introduced Polypropylene Powder for the Fuse Series SLS 3D printers, making end-use quality, highly ductile, and durable polypropylene 3D printed parts accessible. Polypropylene Powder offers an elongation at break of 34% in X/Y directions and 16% in the Z direction, as well as an ultimate tensile strength of 29 MPa, making it nearly identical to injection molded polypropylene. From prototyping to low-volume manufacturing, the Fuse Series and Polypropylene Power enable workflows that eliminate costly tooling and open up new design possibilities.

With its affordable cost, the Fuse Series makes polypropylene SLS 3D printing affordable for product designers, engineers, and manufacturers looking to combine the advantages of polypropylene material with the power of in-house 3D printing. 

Polypropylene 3D printed parts from an SLS 3D printing system are close to isotropic, which means they display similar material properties under stress along all axes. This isotropic quality makes it possible to have 3D printed polypropylene parts function in end-use environments, where force or impact can come from multiple — or unforeseen — directions. FDM printers cannot create isotropic parts, and so FDM 3D printed polypropylene filaments will produce parts that can split under impact along their layer lines. 

SLS 3D printing is a powerful way to prototype, and because polypropylene is so commonly used for consumer goods, SLS 3D printing polypropylene creates opportunities for reimagining consumer products, increasing iterative frequency, and giving small or medium-sized businesses the tools to create parts and bring them to market without outsourcing large parts of their workflow. With end-use quality 3D printed polypropylene parts, the design to manufacturing process is tighter, more efficient, and more cost-effective. 

HP has offered an MJF polypropylene powder material since 2020. MJF customers leverage PP powder’s ability to create true polypropylene parts in order to create continuity in the prototyping and design stages, so that when prototyping turns to mass production, the polypropylene material properties can remain the same throughout. HP’s polypropylene powder offers an elongation at break of 20% and an ultimate tensile strength of 30 MPa, making it similar in performance to the Formlabs Polypropylene Powder for the Fuse Series, but with a slightly less favorable elongation at break.

Only one of the five HP MJF printer models is compatible with their PP powder, so customers should confirm that the right model before purchase.

Printing polypropylene powder parts on the HP MJF printers requires many of the same steps as SLS 3D printing polypropylene. Because many of the MJF printers are larger than the Fuse Series, a packing algorithm should be used to avoid unnecessary powder waste. MJF printers require dedicated electrical circuits, large floor areas, and often a dedicated operator who has been trained in running the machine.

After printing, parts undergo depowdering and media blasting steps, and can then be post-processed with a range of options to achieve an end-use quality finish. These post-processing methods can help take polypropylene parts from prototype to final production quality. 

MJF 3D printing polypropylene delivers parts that accurately represent the material properties of injection molded polypropylene, an important quality for anyone looking to maintain one material throughout the design and production stages. MJF printers create high-quality parts reliably and can be used for production volumes due to their larger build chambers. 

However, MJF printers are costly, and can often cost upwards of $340,000, including annual service contracts, dedicated infrastructure requirements, and expensive powder. 

Many manufacturers offer polypropylene filament options, but they are more expensive than other, more common FDM 3D printing materials such as ABS or PLA filament. The higher HDT of polypropylene means that FDM 3D printers need to maintain a high temperature for both the extruder and print chamber, so it is important to confirm compatiblity before choosing an FDM printer or buying filament to create polypropylene parts.

FDM 3D printed polypropylene isn’t suitable for more advanced applications like end-use parts, where SLS and MJF 3D polypropylene powder excels. There are budget printers capable of printing PP starting at $1,000, mid-range printers that cost approximately $3,500, and industrial systems that start at around $15,000.

Polypropylene filament is harder to print with than standard FDM materials. It requires an extruder temperature of around 240 °C with a bed temperature of 85-120 °C. Printing polypropylene parts on an FDM printer also requires the printer to have a cooling fan — polypropylene filament can warp during the cooling or setting stage, and a fan can help mitigate the risk of this by evenly distributing the cooler air around the part.

FDM 3D printing polypropylene is a good method for creating quick, inexpensive early-stage prototypes or ‘looks-like’ models. The accessibility of many FDM 3D printers, both in cost and workflow, makes it a good technology for hobbyists looking to design consumer goods, or product designers who want an early physical model before starting more intensive design stages. 

FDM 3D printers do not create isotropic or watertight parts, so FDM polypropylene parts can’t effectively function as bottles, enclosures, or tubing, which are common polypropylene applications.

Formlabs offers multiple resins that are ideally suited for prototyping in applications where polypropylene will eventually be used, such as consumer goods packaging. Because there are many different grades of polypropylene, there is more than one resin that can take its place in certain applications. 

Tough 1500 Resin offers very similar material properties to injection molded polypropylene. With an ultimate tensile strength of 33 MPa and an elongation at break of 51%, it’s slightly more flexible than injection molded polypropylene. 

Durable Resin offers similar elongation, at 55%, but a lower ultimate tensile strength at 28 MPa, and more often is used in place of polyethylene materials. 

The workflow for printing polypropylene-like materials with SLA technology depends on printer manufacturer. Printer workflows and costs can range from entry-level costs and easy workflows to complex workflows and high cost machines. Formlabs Form 3+ SLA printers are inexpensive, starting from $2,499, and the workflow is intuitive and clean. 

Once choosing a resin to simulate polypropylene, insert the resin cartridge into the back of the printer and start the print. After the print is done, parts will need to be washed, and, if using Tough 1500 Resin or Durable Resin, will need a post-cure. These two steps can be streamlined using the Formlabs post-processing solutions the Form Wash or Form Wash L and the Form Cure or Form Cure L. 

SLA 3D printing with PP-like materials is ideal for high-quality functional prototypes and prototyping parts normally produced with polypropylene. For SLA customers who are already printing with SLA printers, using Tough 1500 Resin or Durable Resin to simulate polypropylene parts is an easy and inexpensive way to achieve similar mechanical performance. Switching between resins is simple and requires no cleaning step. 

The major downside to printing with these resins is that they are not true polypropylene materials, so there will be some gap in the continuity between design and production if using these for prototyping or design.