The Consistency of Thermoplastics

One of the biggest complaints practitioners have about their field is that the industry is slow to embrace innovation and technology. While other areas of the field have improved their research and development in the hopes of improving their product, as of press time, there is no grant-supported material research for thermoplastics. While the industry seems to be satisfied with the product, the field may not be economically equipped for innovation.


Thermoplastics can be heated in convection or infrared ovens and remolded for a custom fit.
Images: Gary Bedard

Thermoplastics has been an integral material for the O&P industry for decades. The lightweight material has been described as cheaper to make, faster to shape and easier to apply. History shows that thermoplastics fostered a completely new approach to fabrication and the management of forces applied to the body by the concept of total contact, according to Gary Bedard, CO, FAAOP, clinical application liason for Becker Orthopedics.

“That was one of the catch-all terms that was used to promote the material,” Bedard explained. “It was in total contact with the limb and they could build and control within any portion of the device in contact with the limb.”

Bedard believes the application of corrective or stabilizing forces applied to the body through an O&P device became much more intimate and precise, compared to metal and leather devices. Although metal and leather braces still remain somewhat popular among post-polio patients, thermoplastics are generally considered the best choice for bracing and orthotic needs.

“The whole approach, in some respects, changed the nature of the devices from an orthopedic appliance to an orthosis,” Bedard added.


The lightweight material offers the best combination of strength, impact resistance and cost.

For an industry that prides itself on creating custom devices for their patients, the various characteristics of thermoplastics is a major advantage for fabricators and practitioners alike.

“Every single thing we do is custom,” Steve Hill, CO, technical consultant in orthotics for Delphi Ortho and Orthotic and Prosthetic Technological Association member, said. “We can not even use the same mold more than one time for a patient with multiple braces. So we need to find the easiest, most economical way to work and that is with sheet thermoplastic.”

The characteristics of thermoplastics vary from rigid to flexible. They have the ability to be heated and remolded for a perfect custom fit. Thermoplastics cover a wider area of the patient’s limb, while distributing more forces. The lightweight material is also considered economical in both time and cost, Hill added.

The most commonly used thermoplastics are the sheet thermoplastics, polypropylene and polyethylene. Polypropylene is a rigid plastic with many uses in orthotics and prosthetics. Orthotically, polypropylene is durable and heat adjustable, generally between 325°F to 350°F. Polyethylene is lower density, softer and more flexible than polypropylene. Bedard added that polyethylene is used when a fabricator needs a component that has flexibility for tissue containment. He added that polyethylene is generally used in spinal orthoses, inner liners for AFOs and anterior tongue segments for the thigh section of KAFOs. The recommended heat temperature is also 325°F to 350°F.

On the prosthetic side, thermoplastics have been used for soft liners and soft interfaces. They are formed from a thermoplastic material and vacuum thermoforming process. A thermoset composite is still relied upon for the definitive socket, but polyethylene offers a softer response for the patient interface, improving comfort, Bedard noted.

Co-polymer thermoplastics are blended plastics that have a combination of characteristics from polypropylene and polyethylene.

“One of the main thermoplastics we use in orthotics is co-polymer,” Hill said. “Co-polymer is a little bit more flexible and not quite as rigid, but it is more durable and less likely to shatter than polypropylene.”

Thermoplastics have made a fabricators life much easier. However, without the proper bond formulas, quality resin and equipment, such as convection or infrared ovens, and time management skill of an O&P technician, thermoplastic devices are rendered useless.


Thermoplastics have a tendency to pull away from the cosmesis side of the O&P industry. While this may seem irrelevant to some, many patients feel self-conscious when wearing braces and may decide to add a design or color.

For patients who do not like the look of their finished device in its natural state, there is an option to have the thermoplastics pigmented. The pigmented material is a solid color ink. If a pediatric patient would like a team logo or cartoon character on their brace, decorative heat transfers go well with thermoplastics, according to Bedard.

“You probably have as many options with thermoplastics as you do with thermosets because thermoset material must be laminated.”

Hill points out that there are few distributors who sell heat transfer papers, with limited selection of designs.

The economics of innovation

The most recent innovation Hill could recall was thermoplastic elastomer. Thermoplastic elastomer combines rubber and polypropylene that creates a material more resistant to stress and cracking and has a narrow niche in the industry, Hill said.

“I do not believe anyone has identified a need that has not already been built,” Hill said. “It would be nice to have a thinner plastic that is also stronger, but there is only so much we can do.”

Has thermoplastic innovation been maxed out or is the industry just not interested in changing a solid and satisfying product? The answer is not as simple as it seems. The economics is always of great concern, especially in the small O&P market.

“We have not ventured beyond the use of homopolymer polypropylene in the fabrication of O&P devices, as it offers the best combination of strength, impact resistance and cost,” Bedard said. “It is also widely available on a national basis from O&P-specific distributors and regional commercial distributors that can be found in any large metropolitan area.”

The economics do not warrant new innovation. The development of a polypropylene specific to O&P would yield a large expense. The lack of innovation in thermoplastics is based on the large scale of its development. It is difficult to process on a large scale, when most of the materials are custom fitted to a particular patient. A plastic development lab with a lab-scale extruder will cost a high hourly rate for the engineering expertise. Additionally, it is even difficult to find a lab-sized extruder, Bedard explained.

“Resin manufacturers are interested in taking on this project only if you are looking to do 100,000 pounds to the specifications and that does not fit the scale of O&P,” Bedard told O&P Business News.

This would seem unreasonable considering an AFO generally takes only 3 and a half pounds of material, according to Bedard. It is not possible, from an economic standpoint to have an operation that produces sheet stock for the specific use of O&P.

“Consequently, we are forced as a profession and industry to depend on the mass production of sheet stock products that may or may not exactly meet our needs for materials that we custom fabricate into clinical products,” Bedard said.

He added that the polypropylene is specified for general thermoforming needs for many industries, O&P is just one of them. Still, he does not believe the innovation has hit a cap.

“I don’t think the innovation has been maxed out, it is just that our market is so small that it is difficult to attract suppliers that work either in the resin side or the extrusion side with us,” Bedard said. “If you try to develop a polypropylene that was specific to O&P, it entails quite a bit of expenses.”

As research and development persists in the majority of the field, thermoplastics remain the same, while continuing to be a crucial aspect of quality care for the O&P patient. — Anthony Calabro

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