A new wearable device provides the same health benefits as water immersion therapy while drastically cutting down water usage and eliminating the need to go to a fitness center to access communal baths, which can be unhygienic.

Temperature contrast therapy, which traditionally involves immersing the body in a cold water bath, followed by hot water immersion shortly afterwards, has been popularized as a way to speed up recovery after exercising, improve mood, and relieve muscle pain.

According to Xiaoming Tao, the leader of the device’s development team and a professor at Hong Kong Polytechnic University’s Research Institute for Intelligent Wearable Systems, several temperature contrast therapy devices that can be used at home are on the market, but they aren’t ideal.

She says that compared with the current commercial devices, their design allows heat to be transferred more effectively and in much less time — only 10 seconds are needed to switch between hot and cold modes. Their device also provides more coverage than others, which are limited to heating or cooling only a small area of the body.  

The science behind COOLWEAR

The fabric-based device, called COOLWEAR, can transfer heat rapidly due to its fluidic design, meaning it uses flowing water to heat and cool the fabric, which is Velcro-fastened to the limb to be heated or cooled.

Thermoelectric heating and cooling units, which are standard in wearable temperature contrast therapy, are bulky and consume more power, the researchers mentioned in their paper.

“The device works by efficiently cooling or heating the skin through the circulation of cold or warm water within the fluidic channels of the flexible heat-transfer panel,” Tao explained.

The fluidic fabric is made of an ultrathin, waterproof inner layer, which is in direct contact with the skin, a water-circulation channel made of thermoplastic polyurethane as the core layer, and a thermally insulating outer layer. An elastomer tube connects the channels to a small water tank in a portable machine that heats and cools the water.  

Using a smartphone app to activate the temperature therapy program, either warm or cool water is pumped from the tank into the channel in the fabric and then recirculated back into the tank. Each cycle includes a cold mode with a temperature of around 5 °C for one minute and a hot mode at 40 °C for two minutes. In the cold mode, the flowing water absorbs heat from the skin and surroundings, and in hot mode, it dissipates it.

Unlike water immersion therapy, which requires two baths amounting to around 100 liters of water for lower-body immersion, the tank only requires six liters of water to run the device, so the potential water savings is considerable.

Heat-transfer measurements of a device prototype worn on the thigh showed 92% efficiency compared with a cold water immersion bath, where the uniform network pattern of the fluid channel was crucial to the device’s performance.

Tao and her team have adapted the fluidic fabric for use on other parts of the body, such as the ankle and shoulder, which could be challenging. Close contact of the fabric with the skin is crucial to maintaining efficient heat transfer, and the more complex shapes of these joints could lead to poor contact.

To remedy this, they have made the fabric design more ergonomic. 

“We have considered incorporating ergonomic design and elastic bandages to enhance the contact pressure and increase the contact area, ensuring better performance across these complicated body areas,” Tao shared.

Beyond just athletes

The researchers say their device isn’t limited to temperature contrast therapy for athletes and gym-goers. It could potentially be integrated into temperature-controlled suits worn in extreme-temperature environments, used in rehabilitation and healthcare, or to invoke hot and cold sensations during virtual reality games, for example.

However, for the device to be more accessible to individual consumers, its cost would first need to come down.

“Currently, the cost of the device is somewhat high, primarily due to the prototype of the control machine,” Tao said. The fluidic fabric and connection components are much more affordable, she added.

“We are actively working on strategies to reduce costs, particularly for the control machine, through large-scale production in the future,” Tao stated. “Our goal is to make the device accessible to consumers once it is ready for commercialization.”

Reference: Jing Yang, et al. Wearable Fluidic Fabric with Excellent Heat Transfer Performance for Sports Recovery, Advanced Science (2024). DOI: 10.1002/advs.202411691