Underlay Case Study: Reducing Heat and Humidity Inside a Prosthetic Liner
Heat, sweat, and moisture buildup are among the most common challenges experienced by people who wear lower-limb prostheses.
Because a prosthetic socket and liner create a mostly closed environment, heat can accumulate quickly and sweat has very little opportunity to evaporate. As humidity rises, the residual limb may begin to feel hotter, wetter, and less secure inside the liner.
This can contribute to discomfort, odor, friction, skin irritation, liner slippage, and the need to remove the prosthesis during the day.
The Underlay was designed to address this problem directly.
What is the Underlay?
The Underlay is a thin textile sleeve worn against the residual limb, beneath the prosthetic liner.
Its purpose is to help manage:
- Sweat
- Heat
- Humidity
- Odor
- Moisture-related discomfort
The Underlay uses an engineered knitted structure to move moisture away from the skin and direct it toward a breathable mesh area. This creates a pathway for moisture to spread and evaporate more effectively instead of remaining trapped against the residual limb.
The product is also treated with Polygiene StayFresh® technology to help reduce the growth of odor-causing bacteria.
Why humidity matters inside a prosthetic liner
Sweat only cools the body when it can evaporate.
Inside a sealed prosthetic liner, humidity rises and evaporation becomes increasingly difficult. The body may continue producing sweat, but the normal cooling process becomes less effective.
This is why a humid environment often feels much hotter than a dry environment at the same temperature.
By reducing moisture at the skin and supporting evaporation, the Underlay is intended to improve the environment beneath the liner throughout the day.
How the case study was conducted
The Underlay was evaluated by 15 lower-limb amputees, including both transtibial and transfemoral users.
Participants tested the product during daily wear and a variety of physical activities, including:
- Long-distance walking
- Cycling
- Hockey
- Treadmill exercise
- Wheelchair rugby
The study examined perceived humidity, perceived heat, comfort, and measured relative humidity beneath the prosthetic liner.
Read the Full Study Here
Case study results
The results showed meaningful improvements across the participant group.
51% reduction in perceived humidity
Average perceived humidity ratings decreased from 8.4 to 4.1 on a 10-point scale.
This represented a 51% reduction in perceived humidity while wearing the Underlay.
38% reduction in perceived heat
Average perceived heat ratings decreased from 8.3 to 5.2 on a 10-point scale.
This represented a 38% reduction in perceived heat.
17% reduction in measured relative humidity
In addition to user feedback, a controlled sensor-based evaluation measured humidity directly beneath the liner.
The Underlay produced a 17% reduction in measured relative humidity compared with wearing the liner alone.
Humidity also increased more slowly during both the resting and walking phases. This suggests that the Underlay begins managing humidity immediately, rather than only after intense activity begins.
What these findings may mean for prosthetic users
Excessive moisture inside the liner can affect more than comfort.
It may also contribute to:
- Slipping or twisting inside the liner
- Increased friction
- Softening of the skin
- Odor buildup
- Interrupted wear time
- The need to remove and dry the prosthesis during the day
By helping move moisture away from the skin, the Underlay may support a drier and more stable liner environment.
Several participants also reported that they needed to remove their prosthesis less frequently during the day to dry their limb or liner. Users who had previously tried traditional sweat socks commonly described the Underlay as lighter, lower-profile, and more effective at reducing moisture buildup.
Designed for daily integration
The Underlay is designed to fit beneath an existing prosthetic liner without requiring socket modification.
Two configurations are available:
Open-ended Underlay
The open version leaves the distal portion of the limb in direct contact with the liner. This helps preserve direct skin-to-liner contact where it is needed for suspension.
It can also extend beyond the proximal edge of the liner, exposing part of the textile to airflow and supporting evaporation.
Closed Underlay
The closed version covers the distal end of the residual limb and may be preferred depending on the user’s setup, limb shape, and personal preference.
The correct configuration depends on the suspension method, liner length, residual-limb measurements, and individual prosthetic setup.
Supporting suspension
Because the Underlay is worn beneath the liner, suspension was an important part of its development.
Bench testing showed that the Underlay could maintain traction above the estimated force associated with demanding activities such as running when properly positioned.
With the open version, traction exceeded the 90 N running benchmark at 15 cm of liner contact and increased as contact length increased. The closed version also produced traction well above the benchmark in the tested configurations.
This reinforces the importance of proper sizing, positioning, and product selection.
Easy to care for
The Underlay is machine washable and intended for regular use.
It should be washed after each use in water below 40°C with a mild, fragrance-free, bleach-free, and dye-free detergent. It should then be air-dried completely before being worn again.
Because the product must be washed after use, many users choose to keep several Underlays in rotation so they always have a clean, dry one available.
Who may benefit from the Underlay?
The Underlay may be especially relevant for lower-limb prosthetic users who experience:
- Heavy sweating
- Heat buildup
- Moisture beneath the liner
- Odor
- Slippage during activity
- Skin discomfort related to humidity or friction
- Frequent interruptions to remove and dry the prosthesis
It may also be useful for active users, athletes, people working in warm environments, and individuals living in hot or humid climates.
A new approach to prosthetic sweat management
The Underlay was developed to manage moisture while the prosthesis is being worn.
Rather than waiting until sweat has already accumulated, its textile structure continuously moves moisture away from the skin and toward an area where evaporation can occur.
The case study results demonstrate its potential to reduce perceived humidity, reduce perceived heat, improve comfort, and lower measured humidity inside the liner.
For lower-limb amputees dealing with sweat and heat every day, this thin additional layer may make a meaningful difference.
The Underlay is now available directly from Ethnocare.
