Models Made of PUR Foam Instead of Plaster - How the Digital Manufacturing Process Is Transforming Prosthetics and Orthotics

Traditionally, preparing a plaster positive takes anywhere from a few hours to even several working days. Only after this stage can the technician begin the actual inspection of the test tray and make adjustments. Transferring this process to a CAD/CAM environment allows the manual plaster application stage to be completely bypassed in favor of a ready-made model milled from hard foam with a density of at least 70 kg/m³. Where exactly does manual work end and digital support begin, so as not to lose the technician’s invaluable clinical knowledge?

In this article, we compare the two approaches—the traditional plaster process and the modern digital workflow—and show where PUR foam truly lightens the lab’s workload and where the prosthodontist’s experience remains irreplaceable.

How were models for prostheses and orthoses made in the past?

The traditional process of making a prosthetic or orthotic model relied on plaster and manual labor. It consisted of several stages, each of which required time, experience, and appropriate conditions in the laboratory.

The first step was to take a plaster cast directly from the patient’s body: the stump, the limb, or the torso in the case of a corset. The technician applied plaster bands to the patient’s body, which were removed after hardening as a plaster negative. The negative was then filled with plaster to create a positive—a physical, three-dimensional anatomical model.

The positive was subjected to manual processing. The technician adjusted the shape, sculpted relief areas, and added or removed material at critical points to accommodate the patient’s specific biomechanics. A test mold was then made from the model prepared in this way (usually by thermoforming) or a final tray (usually by lamination).

Depending on the level of complexity, the process itself took anywhere from a few hours to a few business days just for the model preparation stage. This does not include the time needed to check the test mold, make any necessary adjustments, and produce the final mold.

Why can the traditional plaster casting process sometimes be problematic?

For decades, the traditional method has been the industry standard, and many experienced prosthodontists continue to create excellent dentures using plaster. Problems with this process rarely affect the final result for an individual patient. Rather, they concern the way a laboratory organizes its work and the production of models on a scale of several dozen or several hundred dentures per year.

• Production time. Each model requires a separate process: applying plaster, drying, forming the negative, filling the positive, and hand-finishing. This takes the technician several hours per model, not counting the subsequent stages.
• Dependence on a specific technician. The quality of the model depends heavily on the experience of the person who makes it. Changing technicians in the middle of the process or the absence of a key employee can slow down the entire plant.
• Difficulty with reproducibility. A second model for the same patient, several years later, whether for a prosthesis replacement or a modification, requires taking a new plaster impression from scratch. There is no recorded reference point.
• Archiving. Plaster casts are heavy, fragile, and take up a lot of space. A dental office that wants to store its patients’ models quickly runs into logistical constraints.
• Remote collaboration. The traditional process requires the patient to be physically present in the lab when measurements are taken and the model to be physically present at the location where the final funnel is manufactured. This makes it difficult to separate the stages of the process and to work with external partners.

What is a digital workflow?

In the digital process, data takes the place of plaster. The sequence is as follows:

1. A 3D scan of the patient. The lab scans the stump, limb, or torso using a body scanner. The scan is saved as an STL file (or another 3D format).
2. Digital model processing. Using CAD/CAM software, the technician modifies the scan: adds relief areas, corrects the shape, and plans the attachment area for the prosthesis or orthosis. All changes are saved in a file and are reversible.
3. CNC milling. The file is sent to a CNC machine, which mills a physical anatomical model from a block of PUR foam based on the file.
4. The workshop's work. The workshop receives a finished model made of PUR foam. It can use this model to create a test funnel using the thermoforming method, a final funnel using the lamination method, or directly produce an orthosis or corset.

Some of the steps (1 and 4) are performed in-house at the prosthetics lab. Others (2 and 3) can be outsourced to a third-party company specializing in digital processing and CNC milling. This allows for a division of labor: the lab focuses on what it does best—interacting with the patient and the final fabrication of the prosthesis—while the digital partner relieves the lab of the manual, time-consuming parts of the process.

What are PUR foam models?

PUR (polyurethane) foam used in prosthetics and orthotics is a rigid structural foam with a minimum density of 70 kg/m³. The material has three characteristics that make it practical for technicians to work with.

• Dimensional stability. The model does not change in size due to temperature and humidity under typical workshop conditions. This means that the milled part retains the geometry designed by the CAD specialist.
• Lightweight. PUR foam is significantly lighter than plaster of comparable volume, which makes it easier to transport and work with. This is particularly important for torso models used with corsets, where the plaster equivalent can weigh over a dozen kilograms.
• Good machinability. The material can be milled with high precision and allows for manual adjustments if the technician wishes to make them after receiving the model. This is important for labs that want to maintain an element of manual work in their process.

The PUR foam model is suitable for thermoforming and lamination without the need to apply a plaster layer, which reduces the workshop’s workload. The technician does not need to prepare additional layers between the model and the final tray, as is sometimes the case with certain other modeling materials.

PUR Foam vs. Plaster – A Practical Comparison

The comparison is not intended to show that one method is “better” than the other in every situation. It highlights the areas where the digital PUR foam process offers real benefits.

Does the digital process replace the prosthetist's expertise?

This question comes up in every conversation with a studio considering a switch to a digital workflow. The short answer: no.

3D scanning, CAD/CAM software, and CNC milling are tools. They replace some of the time-consuming, manual steps in the process where the technician’s expertise was simply wasted: preparing the negative, casting the positive, and mechanically shaping the form. They do not replace what constitutes the core of the prosthetist’s or orthotist’s profession.

In the digital process, clinical decisions are still made by a specialist: patient assessment, selection of the type of prosthesis or orthosis, determination of load and unload zones, and identification of critical areas for biomechanics. Without this knowledge, even the best scan and the best milling will result in a model that does not fulfill its intended function.

In practice, it is clear that the labs that make the best use of digital tools are not those where technology has replaced the prosthodontist. Rather, they are those where the prosthodontist has gained more time for clinical work by reducing the number of less valuable manual procedures. A digital workflow does not replace knowledge—it replaces routine tasks.

Who are PUR foam models designed for?

PUR foam technology is not a solution for every workshop, nor does it benefit all of them equally. The biggest beneficiaries are:

• Prosthetic laboratories that produce a large number of lower-limb prostheses each year—eliminating the manual process results in measurable time savings.
• Orthotic laboratories specializing in AFO, DAFO, and KAFO orthoses and corrective braces—models made of PUR foam work well for thermoforming and lamination.
• Manufacturers of orthopedic supplies who need repeatable models in larger batches or for various clients and workshops.
• Workshops implementing 3D scanning that want to complete the process—they already have a scanner and CAD software, but they need a partner for milling.
• Labs looking to shorten turnaround times—especially those with a patient backlog that exceeds their production capacity.
• Professionals who want to limit their use of plaster—for ergonomic reasons, to maintain studio cleanliness, or for workplace organization.

Laboratories that produce a small number of dentures or specialize in unusual cases—where each model requires an individualized, highly manual assessment—may still find the traditional plaster process to be the most effective. A digital workflow is a tool that makes sense when scale or repeatability give it an advantage.

Neopur – From a 3D Scan to a Finished Model

Neopur manufactures PUR foam models based on 3D scans in STL format or a completed measurement form. The product line covers four main areas:

• PUR foam lower-leg prosthesis models – for laboratories that manufacture lower-leg prostheses.
• PUR foam thigh prosthesis models – for prosthetics laboratories that manufacture thigh prostheses.
• Models of orthoses and orthopedic braces made of PUR foam – for orthotic workshops that work with AFOs, DAFOs, KAFOs, and corrective braces.
• Consulting on scanning and processing 3D models for dental prosthetics – for labs implementing a digital workflow or seeking support for a single, non-standard project.

The workshop sends an STL file or a completed measurement form. Neopur prepares the model digitally, mills it from PUR foam with a minimum density of 70 kg/m³, and ships it to the workshop. The workshop receives the finished model for further processing: thermoforming, lamination, or direct manual processing.

From Plaster to Digital Reproducibility

The traditional plaster process has been the industry standard for years and still has its place in the work of prosthodontists and orthotists, especially in unusual cases where each model requires an individualized, highly manual assessment.

A digital workflow using PUR foam models does not replace this work. Instead, it replaces the time-consuming, manual parts of the process: preparing the negative, casting the positive, manually adjusting the shape, and archiving the physical models. In return, the studio gains repeatability, the ability to work remotely between stages, and a digital record of the model that can be reproduced as needed.

The future of the prosthetist and orthotist’s work does not lie in rejecting artisanal expertise. It lies in combining the specialist’s clinical knowledge with digital technology, CNC, and materials that enable faster and more consistent work.

Do you work in a prosthetics or orthotics lab and are thinking about switching to a digital workflow?

Contact Neopur to discuss your first PUR foam model based on a 3D scan or measurement chart. Together, we’ll determine how best to tailor the process to the specific needs of your studio: from the initial scan, through CAD/CAM processing, to CNC milling and the finished model.