Custom liners: different types, different outcomes
- clement8060
- May 13
- 5 min read
In our field, "Custom Liner" can mean a lot of things... Thermoformable. Custom inner shape but standard outer shape. Custom shape but uniform thicknesses. Injected. Calendered... Although they present very different characteristics, all these products are referred to as "custom liner".
So let's break down the most common manufacturing methods to see clearer through these differences.
Not all Custom Liners are created equal
When we say "custom liners", it's easy to assume they’re all the same — but the reality is far more diverse. Depending on the manufacturing method, each type of custom liner offers distinct features and limitations.
1 - Injected liners
The original way to produce a custom liner consists in making a custom mould in which silicone (or another polymer) is injected.
How it works
First, a physical positive model which copies the shape of the limb is made. This was historically made by plaster casting, but can also be made by scanning the limb and carving in a foam material, 3D printing a positive model, etc. This positive model serves as inside mould component.
Second, a sacrificial layer, typically made of a foam-type materials, is then applied onto the positive model, and ground to obtain the desired liner thickness.
Third, an outside mould component is finally made, typically by vacuum forming a thick thermoplastic sheet onto the [positive + sacrificial layer]
Finally, the sacrificial foam layer is then removed, leaving an empty space between the positive cast and the outer thermoplastic shell, into which silicone (or another polymer) is injected.
PROS | CONS |
|---|---|
Possible to control the local thickness, although thickness control accuracy depends on mould-making method | Once mould is made, the liner shape can not be modified to follow the evolution of the limb. |
Can provide a very good fit | Depending on mould-making method, shape-repeatability can be problematic |
2 - Thermoformable liners
Another traditional way to obtain a custom liner is to work with a liner which elastomer layer is made of a thermoformable material.
How it works
First, a physical positive model which copies the shape of the limb is made (either by plaster casting, scanning the limb and carving in a foam material, 3D printing, etc.)
Second, the liner is placed on the physical copy of the limb and heated for a while. Under the effect of the heat, the thermoformable material takes the shape of the limb copy and retains this shape after cooling down.
PROS | CONS |
|---|---|
Quick and easy to adjust | Final shape can only change to a limited extent from original liner shape. Some limbs can therefore not be fitted. |
Affordable solution | Thicknesses are not customisable |
3 - Liners with custom inside & standard outside
Used by some manufacturers, this process is an evolution of the original injection method described above, which offers a hybrid custom/standard solution.
With this process, the inside surface of the liner is made to fit the limb shape, while the outer surface of the liner presents a standard shape. This standard outer shape facilitates the fitting of a fabric cover and suspension elements, and thereby helps obtaining industrial-grade results.
How it works
First, a 3D scan of the limb is taken.
Second, the 3D scan is modified to fit in a "standardised" outer shape, according to available outer mould sizes. This resulting shape is produced (for example by a foam carving process) to make a inside mould.
Third, the inside mould component is fitted into the standard outer mould component chosen in the previous step, and the liner is injected.
PROS | CONS |
|---|---|
Good fit thanks to custom inside shape | Thicknesses are the result of standard outside - custom inside. They can not be modified / controlled locally. |
Industrial-grade solution enabling quality products at affordable production costs. | Can not fit all limb shapes: limited by the available sizes and shapes of the standardised outside moulds |
4 - HTV silicone liners
Another famous type of custom liners are liners made of "HTV" (high temperature vulcanizing) silicone. This type of silicone comes into a paste-type form, and is therefore not injected, but rather applied in sheets on a positive model to obtain the desired shape and thicknesses.
How it works
First, a positive model of the limb is created.
Second, the HTV silicone (sometimes also refered to as HCR) is calendered (rolled out) between two rolls, to obtain a sheet of paste-like material. By adjusting the space between the two rolls, the thickness of the sheet can be controlled.
Third, the sheet(s) are applied onto the positive model. Several layers can be applied to vary the thickness.
PROS | CONS |
|---|---|
Very good durability | Thicknesses can't be copied if the liner is worn out. Repeatability is limited |
Suitable for patient with high pressure-tolerance, where limb doesn't present sensitive areas. | Hardness is typically much higher, leading to less cushioning / comfort, and harder donning. |
5 - Our Solution: 3D-printed Silicone Liners
Based on the observation that all available methods sometimes fell short, MotionTech developed a proprietary silicone 3D printing technology able to print silicone liners.
This technology was developed specifically to answer the challenges of making prosthetic liners, meaning it is able to accurately print tall objects made of thin walls and soft materials
The local thicknesses and hardness can be varied, and the final product can be reproduced with sub-millimetre accuracy.
With this, Your® Liner was launched on the market in Europe in 2020. The unique possibilities that the technology brings was faced with strong enthusiasm and adoption.
How it works
First, a 3D scan of the limb is taken. The prosthetist configures the liner through MotionTech's ordering platform, choosing the hardness, thicknesses, suspension configuration, aesthetic customisation, etc.
Second, starting from the 3D scan of the limb, MotionTech's CAD team realises the 3D model of the liner. The 3D shape is submitted for validation to the prosthetist to ensure the expected features are well implemented.
Finally, the model is printed and post processed to obtain the final custom liner.
So, what really changes?
Although all of these liners fall under the "custom" umbrella, their capabilities vary dramatically depending on how they’re made. This impacts everything from the comfort and roll-on ability to the possibility of adjusting thicknesses or renewing a liner in the future.
That’s why it's essential to look beyond the label and understand the real capabilities of each technology.
Final Thoughts
Not all custom liners are created equal. While traditional methods still serve important roles, newer technologies like 3D silicone printing offer new levels of adaptability, accuracy, and patient-centered design.
Whether you're a prosthetist deciding on the best solution or a patient trying to understand your options, the key is to look deeper. Ask: What do I need from this liner? What matters most: Thickness control ? Repeatability ? Cost ? Long-term editability ? Local durometer control ?
At MotionTech, when we say custom, we mean 100% custom. But we believe custom shouldn't come at the expense of quality. Your® Liner was therefor built for that: bring unmatched possibilities of functional and aesthetic customisation, whilst striving to deliver industrial-grade quality.
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