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How the RX Shell Is Used to Create a Great Custom Orthotic

There are many different types of orthotics out there to treat a wide range of conditions. All orthotics generally fall into two different categories: Functional and Accommodative.


The choice of materials used to manufacture an orthotic is very important in deciding the device you will get. Functional orthotics are rigid and made from hard materials like plastic and carbon fiber. Accommodative devices are made of soft materials like cork or EVA foams to be more flexible and cushioning.

The goal of a functional device is to control the biomechanics of the foot and provide correction whereas accommodative devices are meant to provide comfort and protection. Because these goals are contradictory, orthotics will usually fall on one side of the spectrum or the other.

About Custom Orthotics:

The main difference between over-the-counter prefabs and custom orthotics is whether or not the device is molded to the patient's foot. A prefabricated orthoses will be made according to shoe size whereas the custom is made to fit the shape of the individual's feet.


Whereas some orthotic labs might cut costs by using a library system to deliver a set range of devices, a true custom orthotics lab will create orthotics built directly to the cast of the patient’s foot. This ensures that no corners are cut and the patient gets a truly custom orthotic made to fit them.

When it comes to accommodative orthotics, layers of soft materials and padding are cut and combined together to match the shape of the foot. These tend to be more bulky, but also more comfortable as the layers provide cushioning and support for the entire bottom of the foot.


Functional orthotics are usually made from thinner, firmer materials focusing on the heel and arch portion of the foot. Traditionally, custom orthotics labs use an extruded flat sheet of thermoplastic such as polypropylene and heat mold it to the shape of the foot. Orthotics made this way are rigid and also create a very device that is the same thickness all the way through.


Benefits of the PRX shell:

One of Forward Motion Medical’s founding goals was to create a thin, strong device that would fit in any shoe and be heat moldable to fit exactly to the patient’s foot.


The end result is now one of our biggest strengths when it comes to making custom orthotics: Performance RX™ shells. A new shell material of our own design that is not only five times stronger than polypropylene, but razor-thin at just 1.5 mm. This allows the material to support extreme forces and still fit in the smallest dress shoe.


Each RX shell is injection molded, which means we are able to have variable thickness in different areas of the shell depending on where it is needed. This means we can control where it’s thin, where it’s thick, how thick it is, and basically gives us the ability to engineer an arch to flex exactly how we want it to flex. Injected molded shells also retain their shape better than those that are molded from a flat piece of thermoplastic.

Orthotics made of soft materials will eventually wear down to the point where they no longer provide support and need to be replaced. Even thermoplastics and polypropylene are known to flatten out over prolonged usage. RX shells do not have this problem and are guaranteed to never change shape or flatten.


RX shells can be re-heated and re-adjusted, and are non-toxic to heat and grinding making them safe and easy to customize. Furthermore, they come in 4 different rigidities which means they can be as functional or accommodative as needed depending on the conditions. RX shells give doctors the ability to determine flexibility and comfort, which leads to a greater range of combinations to treat patient needs.

If the patient is older and has sensitive feet? Prescribe a semi-flex shell combined with more padding or softer top cover material. Is the patient heavier and need more correction and control? Increase shell rigidity, deepen the heel cup, and add extrinsic posting.


To Summarize:

​Traditional Orthotic Materials

Performance RX™ Shells

Large and bulky

Thin and light

Same thickness throughout

Variable Thickness

Flattens out over time

Never lose shape

Can’t control rigidity

Different rigidities available

Either flexible or supportive

Flexible while still supportive

Instead of being limited by materials and having to decide between completely functional or completely accommodative, PRX shells allow for an orthotic device that is a combination of function and accommodation. They provide the maximum benefit and comfort for your patients while still being thinner, lighter, and more controlled than other orthotic materials.


Whatever your patients need in a custom orthotic, we got them covered at Forward Motion Medical! If you have any questions, please feel free to contact us. We make orthotics that your parents will love to wear!


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1 Comment


Great Article; I will pass it onto students attending the RMPI.

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